"Mybatis 中表与表之间的关系分为一下 4 类： 1）一对一 2）一对多 3）多对一 4）多对多创建数据 Demo 表数据库表：用户表 user：记录了购买商品的用户信息。订单表 orders：记录了用户所创建的订单（购买商品的订单）。订单明细表 orderdetail：记录了订单的详 ...."

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MyBatis(五)：mybatis关联映射

Mybatis 中表与表之间的关系分为一下 4 类：

1）一对一

2）一对多

3）多对一

4）多对多

创建数据 Demo 表

数据库表：

用户表 user：记录了购买商品的用户信息。

订单表 orders：记录了用户所创建的订单（购买商品的订单）。

订单明细表 orderdetail：记录了订单的详细信息即购买商品的信息。

商品表 items：记录商品信息。

数据模型：

数据表之间的关系：

先分析数据级别之间有关系的表之间的业务关系：

usre 和 orders：

user —-> orders：一个用户可以创建多个订单，一对多
orders —-> user：一个订单只由一个用户创建，一对一

orders 和 orderdetail：

orders —-> orderdetail：一个订单可以包括多个订单明细，因为一个订单可以购买多个商品，每个商品的购买信息在 orderdetail 记录，一对多关系。
orderdetail —-> orders：一个订单明细只能包括在一个订单中，一对一

orderdetail 和 itesm：

orderdetail —-> itesms：一个订单明细只对应一个商品信息，一对一
items —-> orderdetail: 一个商品可以包括在多个订单明细，一对多

创建 Demo 表

/*
Navicat MySQL Data Transfer
Source Server         : mysql1
Source Server Version : 50712
Source Host           : localhost:3306
Source Database       : relation
Target Server Type    : MYSQL
Target Server Version : 50712
File Encoding         : 65001
Date: 2019-03-24 15:57:05
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for items
-- ----------------------------
DROP TABLE IF EXISTS items;
CREATE TABLE items (
items_id int(11) NOT NULL AUTO_INCREMENT,
name varchar(64) DEFAULT NULL,
price double(10,2) DEFAULT NULL,
detail varchar(255) DEFAULT NULL,
pic varchar(255) DEFAULT NULL,
createtime date DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of items
-- ----------------------------
INSERT INTO items VALUES ('1', '巧克力', '28.00', '黑巧克力', 'pic url', '2019-01-01');
INSERT INTO items VALUES ('2', '运动袜', '35.00', '运动袜', 'pic url', '2019-01-01');
INSERT INTO items VALUES ('3', '高跟鞋', '890.00', '高跟鞋', 'pic url', '2019-01-01');
-- ----------------------------
-- Table structure for orders
-- ----------------------------
DROP TABLE IF EXISTS orders;
CREATE TABLE orders (
id int(11) NOT NULL AUTO_INCREMENT,
</span><span style="color: rgba(255, 0, 255, 1)">user_id</span> int(11) DEFAULT NULL,
</span><span style="color: rgba(0, 0, 255, 1)">number</span> int(11) DEFAULT NULL,
createtime date DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of orders
-- ----------------------------
INSERT INTO orders VALUES ('1', '1', '2', '2019-03-24');
INSERT INTO orders VALUES ('2', '2', '1', '2019-03-22');
INSERT INTO orders VALUES ('3', '2', '2', '2019-03-24');
-- ----------------------------
-- Table structure for ordersdetail
-- ----------------------------
DROP TABLE IF EXISTS ordersdetail;
CREATE TABLE ordersdetail (
ordersdetail_id int(11) NOT NULL AUTO_INCREMENT,
items_id int(11) DEFAULT NULL,
items_num int(11) DEFAULT NULL,
orders_id int(11) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of ordersdetail
-- ----------------------------
INSERT INTO ordersdetail VALUES ('1', '1', '1', '1');
INSERT INTO ordersdetail VALUES ('2', '2', '1', '1');
INSERT INTO ordersdetail VALUES ('3', '1', '1', '2');
INSERT INTO ordersdetail VALUES ('4', '2', '1', '3');
INSERT INTO ordersdetail VALUES ('5', '3', '1', '3');
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS <span style="color: rgba(255, 0, 255, 1)">user</span><span style="color: rgba(0, 0, 0, 1)">;
CREATE TABLE <span style="color: rgba(255, 0, 255, 1)">user</span><span style="color: rgba(0, 0, 0, 1)"> (
id int(11) NOT NULL AUTO_INCREMENT,
username varchar(32) DEFAULT NULL,
birthday date DEFAULT NULL,
address varchar(255) DEFAULT NULL,
gender varchar(4) DEFAULT NULL,
PRIMARY KEY (id),
UNIQUE KEY idx_username (username)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO <span style="color: rgba(255, 0, 255, 1)">user</span> VALUES ('1', 'zhangsan', '1999-10-01', '北京市海淀区海淀黄庄', '男');
INSERT INTO <span style="color: rgba(255, 0, 255, 1)">user</span> VALUES ('2', 'lili', '1989-02-02', '北京市朝阳区大运村', '女');

配置 mybatis-generator 插件，生成 mapper、mapper.xml、model 代码:

第一步：创建 demo maven 项目：

填写 Group Id、Artifact Id、Packaging 选择为 pom：

此时项目值包含 mybatie-study

然后，创建 maven module------- 选中 mybatie-study maven 项目，然后右键 -》弹出菜单，菜单中选择 New-> 选择 Other...

在弹出 New 窗口中选择 Maven->Maven Module

填写 Maven Module 名称

点击 finish 完成 Maven Module 创建。

第二步：在 Maven Module 项目 mybatis-relation 下 /src/main/resources 目录下，创建 generatorConfig.xml 文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE generatorConfiguration PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN" "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd" >
<generatorConfiguration>
    <!-- jdbc 连接库 jar 包路径 -->
    <classPathEntry location="D:\IDE\maven\repository\mysql\mysql-connector-java\5.1.38\mysql-connector-java-5.1.38.jar" />
    <!-- eclipse tool 配置 Location = E:\Java\apache-maven-3.2.3\bin\mvn.bat Working 
        Direction = ${workspace_loc:/linetoy-common} Arguments = mybatis-generator:generate -->
    <context id="DB2Tables" targetRuntime="MyBatis3">
        <!-- 去掉注释，一般都会去掉，那个注释真的不敢让人恭维 -->
        <commentGenerator>
            <property name="suppressAllComments" value="true" />
        </commentGenerator>
        <!-- jdbc 连接配置 -->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
            connectionURL="jdbc:mysql://localhost:3306/relation?characterEncoding=UTF-8" userId="root"
            password="root">
        </jdbcConnection>
        <!-- 数字字段是否强制使用 BigDecimal 类 -->
        <javaTypeResolver>
            <property name="forceBigDecimals" value="false" />
        </javaTypeResolver>
        <!-- entity 创建后放在那个项目的哪个包路径上 -->
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">javaModelGenerator </span><span style="color: rgba(255, 0, 0, 1)">targetPackage</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.model"</span><span style="color: rgba(255, 0, 0, 1)">
        targetProject</span><span style="color: rgba(0, 0, 255, 1)">="D:\git\springboot_learn01\mybatie-study\mybatis-relation\src\main\java"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">property </span><span style="color: rgba(255, 0, 0, 1)">name</span><span style="color: rgba(0, 0, 255, 1)">="enableSubPackages"</span><span style="color: rgba(255, 0, 0, 1)"> value</span><span style="color: rgba(0, 0, 255, 1)">="true"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">property </span><span style="color: rgba(255, 0, 0, 1)">name</span><span style="color: rgba(0, 0, 255, 1)">="trimStrings"</span><span style="color: rgba(255, 0, 0, 1)"> value</span><span style="color: rgba(0, 0, 255, 1)">="true"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">javaModelGenerator</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span> 
    
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> dao创建后放在那个项目的哪个包路径上 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">sqlMapGenerator </span><span style="color: rgba(255, 0, 0, 1)">targetPackage</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.dao"</span><span style="color: rgba(255, 0, 0, 1)">
        targetProject</span><span style="color: rgba(0, 0, 255, 1)">="D:\git\springboot_learn01\mybatie-study\mybatis-relation\src\main\java"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">property </span><span style="color: rgba(255, 0, 0, 1)">name</span><span style="color: rgba(0, 0, 255, 1)">="enableSubPackages"</span><span style="color: rgba(255, 0, 0, 1)"> value</span><span style="color: rgba(0, 0, 255, 1)">="true"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">sqlMapGenerator</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> dao的.xml描述sql文件创建后放在那个项目的哪个包路径上 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">javaClientGenerator </span><span style="color: rgba(255, 0, 0, 1)">type</span><span style="color: rgba(0, 0, 255, 1)">="XMLMAPPER"</span><span style="color: rgba(255, 0, 0, 1)">
        targetPackage</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.dao"</span><span style="color: rgba(255, 0, 0, 1)">
        targetProject</span><span style="color: rgba(0, 0, 255, 1)">="D:\git\springboot_learn01\mybatie-study\mybatis-relation\src\main\java"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">property </span><span style="color: rgba(255, 0, 0, 1)">name</span><span style="color: rgba(0, 0, 255, 1)">="enableSubPackages"</span><span style="color: rgba(255, 0, 0, 1)"> value</span><span style="color: rgba(0, 0, 255, 1)">="true"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">javaClientGenerator</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 要生成的表配置，可以多个 tableName：表名 domainObjectName：指定类名 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">table </span><span style="color: rgba(255, 0, 0, 1)">tableName</span><span style="color: rgba(0, 0, 255, 1)">="orders"</span><span style="color: rgba(255, 0, 0, 1)"> domainObjectName</span><span style="color: rgba(0, 0, 255, 1)">="Orders"</span><span style="color: rgba(255, 0, 0, 1)">
        enableCountByExample</span><span style="color: rgba(0, 0, 255, 1)">="false"</span><span style="color: rgba(255, 0, 0, 1)"> enableUpdateByExample</span><span style="color: rgba(0, 0, 255, 1)">="false"</span><span style="color: rgba(255, 0, 0, 1)">
        enableDeleteByExample</span><span style="color: rgba(0, 0, 255, 1)">="false"</span><span style="color: rgba(255, 0, 0, 1)"> enableSelectByExample</span><span style="color: rgba(0, 0, 255, 1)">="false"</span><span style="color: rgba(255, 0, 0, 1)">
        selectByExampleQueryId</span><span style="color: rgba(0, 0, 255, 1)">="false"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
          <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">generatedKey </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="id"</span><span style="color: rgba(255, 0, 0, 1)"> sqlStatement</span><span style="color: rgba(0, 0, 255, 1)">="Mysql"</span><span style="color: rgba(255, 0, 0, 1)"> identity</span><span style="color: rgba(0, 0, 255, 1)">="true"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">table</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">context</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

</generatorConfiguration>

该配置文件用来配置生成 mybatis 代码规则，以及代码生成目录，将要生成代码的 table 配置。

第三步：在 Maven Module 项目 mybatis-relation 中 pom.xml 中引入依赖包：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.dx.mybatis01</groupId>
        <artifactId>mybatie-study</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <groupId>com.dx.mybatis01.relation</groupId>
    <artifactId>mybatis-relation</artifactId>
<span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">dependencies</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 配置mybatis的开发包 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>org.mybatis<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>mybatis<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>3.4.1<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 配置mysql支持包 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> https://mvnrepository.com/artifact/mysql/mysql-connector-java </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>mysql<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>mysql-connector-java<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>5.1.38<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>          
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 日志 slf4j是规范/接口 日志实现:log4j,logback,common-logging 这里使用:slf4j + log4j </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>org.slf4j<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>slf4j-log4j12<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>1.7.2<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> https://mvnrepository.com/artifact/org.mybatis.generator/mybatis-generator-core </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>org.mybatis.generator<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>mybatis-generator-core<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>1.3.5<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">dependency</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            
<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">dependencies</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">build</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">defaultGoal</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>compile<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">defaultGoal</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">finalName</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>mybatis-plugin<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">finalName</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">plugins</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">plugin</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>org.apache.maven.plugins<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>maven-surefire-plugin<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>2.1<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">configuration</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">skip</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>true<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">skip</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">configuration</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">plugin</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">plugin</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>org.mybatis.generator<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">groupId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>mybatis-generator-maven-plugin<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">artifactId</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>1.3.5<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">version</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">configuration</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>   
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">configurationFile</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>${basedir}/src/main/resources/generatorConfig.xml<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">configurationFile</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">verbose</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>true<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">verbose</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">overwrite</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>true<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">overwrite</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">configuration</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">plugin</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">plugins</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">build</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

</project>

第四步：选中 Maven Module 项目右键运行生成 mybatis 代码：

在 Maven build..... 弹出窗口中，Global 参数中填写“mybatis-generator:generate”，并运行

执行日志：

Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-11T00:41:47+08:00)
Maven home: D:\Java_Study\apache-maven-3.3.9
Java version: 1.8.0_161, vendor: Oracle Corporation
Java home: C:\Program Files\Java\jdk1.8.0_161\jre
Default locale: zh_CN, platform encoding: GBK
OS name: "windows 7", version: "6.1", arch: "amd64", family: "dos"
[DEBUG] Created new class realm maven.api
[DEBUG] Importing foreign packages into class realm maven.api
。。。。。。
[DEBUG] Populating class realm maven.api
[INFO] Error stacktraces are turned on.
[DEBUG] Reading global settings from D:\Java_Study\apache-maven-3.3.9\conf\settings.xml
[DEBUG] Reading user settings from D:\Java_Study\apache-maven-3.3.9\conf\settings.xml
[DEBUG] Reading global toolchains from D:\Java_Study\apache-maven-3.3.9\conf\toolchains.xml
[DEBUG] Reading user toolchains from C:\Users\Administrator\.m2\toolchains.xml
[DEBUG] Using local repository at D:\IDE\maven\repository
[DEBUG] Using manager EnhancedLocalRepositoryManager with priority 10.0 for D:\IDE\maven\repository
[INFO] Scanning for projects...
[DEBUG] Using mirror nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) for central (https://repo.maven.apache.org/maven2).
[DEBUG] Extension realms for project com.dx.mybatis01.relation:mybatis-relation🏺0.0.1-SNAPSHOT: (none)
[DEBUG] Looking up lifecyle mappings for packaging jar from ClassRealm[plexus.core, parent: null]
[DEBUG] Extension realms for project com.dx.mybatis01:mybatie-study:pom:0.0.1-SNAPSHOT: (none)
[DEBUG] Looking up lifecyle mappings for packaging pom from ClassRealm[plexus.core, parent: null]
[DEBUG] Resolving plugin prefix mybatis-generator from [org.apache.maven.plugins, org.codehaus.mojo]
[DEBUG] Using mirror nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) for snapshots (http://snapshots.maven.codehaus.org/maven2).
[DEBUG] Resolved plugin prefix mybatis-generator to org.mybatis.generator:mybatis-generator-maven-plugin from POM com.dx.mybatis01.relation:mybatis-relation🏺0.0.1-SNAPSHOT
[DEBUG] === REACTOR BUILD PLAN ================================================
[DEBUG] Project: com.dx.mybatis01.relation:mybatis-relation🏺0.0.1-SNAPSHOT
[DEBUG] Tasks:   [mybatis-generator:generate]
[DEBUG] Style:   Regular
[DEBUG] =======================================================================
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building mybatis-relation 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[DEBUG] Resolving plugin prefix mybatis-generator from [org.apache.maven.plugins, org.codehaus.mojo]
[DEBUG] Resolved plugin prefix mybatis-generator to org.mybatis.generator:mybatis-generator-maven-plugin from POM com.dx.mybatis01.relation:mybatis-relation🏺0.0.1-SNAPSHOT
[DEBUG] Lifecycle default -> [validate, initialize, generate-sources, process-sources, generate-resources, process-resources, compile, process-classes, generate-test-sources, process-test-sources, generate-test-resources, process-test-resources, test-compile, process-test-classes, test, prepare-package, package, pre-integration-test, integration-test, post-integration-test, verify, install, deploy]
[DEBUG] Lifecycle clean -> [pre-clean, clean, post-clean]
[DEBUG] Lifecycle site -> [pre-site, site, post-site, site-deploy]
[DEBUG] === PROJECT BUILD PLAN ================================================
[DEBUG] Project:       com.dx.mybatis01.relation:mybatis-relation:0.0.1-SNAPSHOT
[DEBUG] Dependencies (collect): []
[DEBUG] Dependencies (resolve): []
[DEBUG] Repositories (dependencies): [nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public, default, releases)]
[DEBUG] Repositories (plugins)     : [nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public, default, releases)]
[DEBUG] -----------------------------------------------------------------------
[DEBUG] Goal:          org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate (default-cli)[DEBUG] Style:         Regular
[DEBUG] Configuration: <?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <configurationFile default-value="${project.basedir}/src/main/resources/generatorConfig.xml">D:\git\springboot_learn01\mybatie-study\mybatis-relation/src/main/resources/generatorConfig.xml</configurationFile>
  <contexts>${mybatis.generator.contexts}</contexts>
  <jdbcDriver>${mybatis.generator.jdbcDriver}</jdbcDriver>
  <jdbcPassword>${mybatis.generator.jdbcPassword}</jdbcPassword>
  <jdbcURL>${mybatis.generator.jdbcURL}</jdbcURL>
  <jdbcUserId>${mybatis.generator.jdbcUserId}</jdbcUserId>
  <outputDirectory default-value="${project.build.directory}/generated-sources/mybatis-generator">${mybatis.generator.outputDirectory}</outputDirectory>
  <overwrite default-value="false">true</overwrite>
  <project>${project}</project>
  <skip default-value="false">${mybatis.generator.skip}</skip>
  <sqlScript>${mybatis.generator.sqlScript}</sqlScript>
  <tableNames>${mybatis.generator.tableNames}</tableNames>
  <verbose default-value="false">true</verbose>
</configuration>
[DEBUG] =======================================================================
[INFO] 
[INFO] --- mybatis-generator-maven-plugin:1.3.5:generate (default-cli) @ mybatis-relation ---
[DEBUG] Using mirror nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) for apache.snapshots (http://repository.apache.org/snapshots).
[DEBUG] Using mirror nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) for sonatype-nexus-snapshots (https://oss.sonatype.org/content/repositories/snapshots).
[DEBUG] Using mirror nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) for repository.jboss.org (http://repository.jboss.org/maven2).
[DEBUG] Using mirror nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) for snapshots.jboss.org (http://snapshots.jboss.org/maven2).
[DEBUG] Using mirror nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) for oss.sonatype.org/jboss-snapshots (http://oss.sonatype.org/content/repositories/jboss-snapshots).
[DEBUG] Dependency collection stats: {ConflictMarker.analyzeTime=1, ConflictMarker.markTime=0, ConflictMarker.nodeCount=17, ConflictIdSorter.graphTime=0, ConflictIdSorter.topsortTime=1, ConflictIdSorter.conflictIdCount=14, ConflictIdSorter.conflictIdCycleCount=0, ConflictResolver.totalTime=2, ConflictResolver.conflictItemCount=17, DefaultDependencyCollector.collectTime=739, DefaultDependencyCollector.transformTime=5}
[DEBUG] org.mybatis.generator:mybatis-generator-maven-plugin🏺1.3.5:
。。。。。。
[DEBUG] Configuring mojo org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate from plugin realm ClassRealm[plugin>org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5, parent: sun.misc.Launcher$AppClassLoader@33909752]
[DEBUG] Configuring mojo 'org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate' with basic configurator -->
[DEBUG]   (f) configurationFile = D:\git\springboot_learn01\mybatie-study\mybatis-relation\src\main\resources\generatorConfig.xml
[DEBUG]   (f) outputDirectory = D:\git\springboot_learn01\mybatie-study\mybatis-relation\target\generated-sources\mybatis-generator
[DEBUG]   (f) overwrite = true
[DEBUG]   (f) project = MavenProject: com.dx.mybatis01.relation:mybatis-relation:0.0.1-SNAPSHOT @ D:\git\springboot_learn01\mybatie-study\mybatis-relation\pom.xml
[DEBUG]   (f) skip = false
[DEBUG]   (f) verbose = true
[DEBUG] -- end configuration --
[INFO] Connecting to the Database
Sun Mar 24 14:42:43 CST 2019 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
[INFO] Introspecting table orders
[DEBUG] Retrieving column information for table "orders"
[DEBUG] Found column "id", data type 4, in table "relation..orders"
[DEBUG] Found column "user_id", data type 4, in table "relation..orders"
[DEBUG] Found column "number", data type 4, in table "relation..orders"
[DEBUG] Found column "createtime", data type 91, in table "relation..orders"
[INFO] Generating Record class for table orders
[INFO] Generating Mapper Interface for table orders
[INFO] Generating SQL Map for table orders
[INFO] Saving file OrdersMapper.xml
[INFO] Saving file Orders.java
[INFO] Saving file OrdersMapper.java
[WARNING] Existing file D:\git\springboot_learn01\mybatie-study\mybatis-relation\src\main\java\com\dx\mybatis01\model\Orders.java was overwritten
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.499 s
[INFO] Finished at: 2019-03-24T14:42:44+08:00
[INFO] Final Memory: 19M/491M
[INFO] ------------------------------------------------------------------------

刷新项目，此时可以发现项目中已经包含了新的代码生成：

一对一查询

实例：查询订单信息，关联查询创建订单的用户信息。

SELECT 
orders.*,user.username,user.gender,user.address 
FROM orders,USER 
WHERE orders.user_id = user.id

主查询表：orders
关联查询表：user
联结查询：内联结

利用 ResultType

1、SQL 语句的书写要领：先确定查询的主表，在确定查询的关联表，关联查询是使用内联结还是外联结。
2、POVO 扩展类创建。(这是由于关联查询出来的信息是多张表的综合字段，所以我们可以根据 POJO 创建我们的扩展类)
3、Mapper.xml 和 Mapper.java 的代理编写
4、进行测试

在 Maven Module 项目 mybatis-relation 下 src/main/resources 下创建 mybatis.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <setting name="cacheEnabled" value="true"/>
    </settings>
    <typeAliases>
        <!-- <typeAlias type="com.demo.module.News" alias="News"/> -->
    </typeAliases>
    <environments default="development"> 
        <!-- 配置数据源的相关信息 -->
        <environment id="development">
            <transactionManager type="jdbc" /> <!-- 使用 JDBC 方式管理 -->
            <dataSource type="POOLED"> <!-- 设置数据源类型，此时为 POOLED -->
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/relation" />
                <!-- 设置数据库连接的用户名和密码 -->
                <property name="username" value="root" />
                <property name="password" value="root" /> 
            </dataSource> 
        </environment>
    </environments>
    <mappers>
          <mapper resource="com/dx/mybatis01/dao/OrdersExtendsMapper.xml"></mapper>
    </mappers>
</configuration>

在 com.dx.mybatis01.module 下创建 module：

Order.java

package com.dx.mybatis01.model;
import java.util.Date;
import java.util.List;
public class Orders {
private Integer id;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Integer userId;

</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Integer number;

</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Date createtime;  
</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 用户信息</span>
<span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> User user;       
</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">商品信息存放集合</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> List&lt;OrdersDetail&gt;<span style="color: rgba(0, 0, 0, 1)"> orderdetails;   

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> User getUser() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> user;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setUser(User user) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.user =<span style="color: rgba(0, 0, 0, 1)"> user;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> List&lt;OrdersDetail&gt;<span style="color: rgba(0, 0, 0, 1)"> getOrderdetails() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> orderdetails;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> setOrderdetails(List&lt;OrdersDetail&gt;<span style="color: rgba(0, 0, 0, 1)"> orderdetails) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.orderdetails =<span style="color: rgba(0, 0, 0, 1)"> orderdetails;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Integer getId() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> id;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setId(Integer id) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.id =<span style="color: rgba(0, 0, 0, 1)"> id;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Integer getUserId() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> userId;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setUserId(Integer userId) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.userId =<span style="color: rgba(0, 0, 0, 1)"> userId;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Integer getNumber() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> number;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setNumber(Integer number) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.number =<span style="color: rgba(0, 0, 0, 1)"> number;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Date getCreatetime() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> createtime;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setCreatetime(Date createtime) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.createtime =<span style="color: rgba(0, 0, 0, 1)"> createtime;
}

}

View Code

OrdersExtends.java

package com.dx.mybatis01.model;
public class OrdersExtends extends Orders{
private String username;
private String gender;
private String address;
......
}

在 com.dx.mybatis01.dao 下创建 mapper 和 mapper.xml：

OrdersExtendsMapper.java

package com.dx.mybatis01.dao;
import java.util.List;
import com.dx.mybatis01.model.OrdersExtends;
public interface OrdersExtendsMapper {
List<OrdersExtends>  findOrderAndUser();
}

OrdersExtendsMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dx.mybatis01.dao.OrdersExtendsMapper">
  <select id="findOrderAndUser" resultType="com.dx.mybatis01.model.OrdersExtends">
      SELECT 
          orders.*,user.username,user.gender,user.address 
      FROM orders,USER 
      WHERE orders.user_id = user.id
  </select>
</mapper>

测试类：

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.dx.mybatis01.dao.OrdersExtendsMapper;
import com.dx.mybatis01.model.OrdersExtends;
public class OrdersExtendsTest {
private SqlSessionFactory sqlSessionFactory = null;
private SqlSession session = null;
@Before
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> Init() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> IOException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 加载总配置文件，转化为流</span>
    String resource = "mybatis.cfg.xml"<span style="color: rgba(0, 0, 0, 1)">;
    InputStream inputStream </span>=<span style="color: rgba(0, 0, 0, 1)"> Resources.getResourceAsStream(resource);

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建sqlSessionFactory</span>
    sqlSessionFactory = <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactoryBuilder().build(inputStream);
    session </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
}

@After
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> destory() {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.session.close();
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> test() {
    OrdersExtendsMapper ordersExtendsMapper </span>= session.getMapper(OrdersExtendsMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    List</span>&lt;OrdersExtends&gt; list =<span style="color: rgba(0, 0, 0, 1)"> ordersExtendsMapper.findOrderAndUser();
    </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)"> (OrdersExtends o : list) {
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> getUserid没有和数据库对应，所以无法获取默认为null</span>
        System.out.println(o.getId() + ":" + o.getUserId() + ":" + o.getUsername() + ":" +<span style="color: rgba(0, 0, 0, 1)"> o.getAddress());
    }
}

}

输出：

1:null:zhangsan: 北京市海淀区海淀黄庄
2:null:lili: 北京市朝阳区大运村
3:null:lili: 北京市朝阳区大运村

注意：上述测试代码中，由于 userid 没有和数据库中的字段进行对应 (user_id)，所以会造成数据映射不成功而默认为 null。

项目代码结构如下：

利用 ResultMap

思路：利用 ResultMap 有点类似于 Hibernate 中 POJO 类中的设置。将我们对应的属性关联到类中。
1、使用 resultMap 将查询结果中的订单信息映射到 Orders 对象中，
2、在 orders 类中添加 User 属性，将关联查询出来的用户信息映射到 orders 对象中的 user 属性中。
Order.java

public class Orders {
    private Integer id;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Integer userId;

</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Integer number;

</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Date createtime;  
</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 用户信息</span>
<span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> User user;       
......

}

OrderMapper 和 Mapper xml 如下：

OrderMapper.java

package com.dx.mybatis01.dao;
import java.util.List;
import com.dx.mybatis01.model.Orders;
public interface OrdersMapper {
List<Orders> findOrderAndUserResultMap();
}

OrdersMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dx.mybatis01.dao.OrdersMapper">
  <!-- 订单查询关联用户的查询 -->
  <resultMap type="com.dx.mybatis01.model.Orders" id="OrderUserResultMap">
    <!-- 配置映射的订单信息 -->
    <id column="id" property="id"/>
     <result column="user_id" property="userId"/>      
    <result column="number" property="number"/>
    <result column="createtime" property="createtime"/>
    <result column="note" property="note"/>
<span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 配置关联的用户信息
    association:用来映射关联查询单个对象的信息
    property ：将关联信息映射到Order的哪个属性中去
    javaType 映射到那个java类中
  </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">association </span><span style="color: rgba(255, 0, 0, 1)">property</span><span style="color: rgba(0, 0, 255, 1)">="user"</span><span style="color: rgba(255, 0, 0, 1)"> javaType</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.model.User"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> id  关联查询用户的唯一标识 ，外键 column 指定唯一标识用户信息的字段，property表示类中属性 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">id </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="id"</span><span style="color: rgba(0, 0, 255, 1)">/&gt;</span>             
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="username"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="username"</span><span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="gender"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="gender"</span><span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="address"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="address"</span><span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">association</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

</resultMap>
<select id="findOrderAndUserResultMap" resultMap="OrderUserResultMap">
SELECT orders.*,user.username,user.gender,user.address
FROM orders,USER
WHERE orders.user_id = user.id
</select>
</mapper>

测试类：

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.dx.mybatis01.dao.OrdersMapper;
import com.dx.mybatis01.model.Orders;
public class OrdersMapperTest {
private SqlSessionFactory sqlSessionFactory = null;
private SqlSession session = null;
@Before
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> Init() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> IOException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 加载总配置文件，转化为流</span>
    String resource = "mybatis.cfg.xml"<span style="color: rgba(0, 0, 0, 1)">;
    InputStream inputStream </span>=<span style="color: rgba(0, 0, 0, 1)"> Resources.getResourceAsStream(resource);

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建sqlSessionFactory</span>
    sqlSessionFactory = <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactoryBuilder().build(inputStream);
    session </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
}

@After
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> destory() {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.session.close();
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> test() {
    OrdersMapper ordersExtendsMapper </span>= session.getMapper(OrdersMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    List</span>&lt;Orders&gt; list =<span style="color: rgba(0, 0, 0, 1)"> ordersExtendsMapper.findOrderAndUserResultMap();
    </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)"> (Orders o : list) {
        System.out.println(o.getId() </span>+ ":" + o.getUserId() + ":" + o.getUser().getUsername() + ":" +<span style="color: rgba(0, 0, 0, 1)"> o.getUser().getAddress());
    }
}

}

测试打印信息：

1:1:zhangsan: 北京市海淀区海淀黄庄
2:2:lili: 北京市朝阳区大运村
3:2:lili: 北京市朝阳区大运村

说明：
利用 ResultMap，我们可以利用其中的 association 属性将外键关联的相关类进行映射。这也是使用 ResultMap 的便利之一。

ResultType 和 ResultMap 实现一对一查询比较
1、resultType：使用 resultType 实现较为简单，如果 pojo 中没有包括查询出来的列名，需要增加列名对应的属性，即可完成映射。如果没有查询结果的特殊要求建议使用 resultType。
2、resultMap：需要单独定义 resultMap，实现有点麻烦，如果对查询结果有特殊的要求，使用 resultMap 可以完成将关联查询映射 pojo 的属性中。
3、resultMap 可以实现延迟加载，resultType 无法实现延迟加载。

一对多查询

实例：查询订单及订单明细的信息。

        SELECT
            t10.id,t10.user_id,t10.number,t10.createtime,
            t11.username,t11.gender,t11.address,
            t12.ordersdetail_id,t12.items_id,t12.items_num,t12.orders_id
        FROM orders t10
        inner join USER t11 on t10.user_id=t11.id
        left outer join ordersdetail t12 on t10.id=t12.orders_id

主查询表：orders
确定关联查询表：orderdetail
联结查询：内联结

利用 resultType 将上边的查询结果映射到 pojo 中，订单信息的就是重复。而我们对于对 orders 映射不能出现重复记录。所以我们这里只能利用 ResultMap。

利用 ResultMap

POJO 类

// POJO 类
    public class User {
        private int id;
        private String username;
        private Date birthday;
        private String address;
        private String gender;
    }
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)"> Orders {

    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> User user;

    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> id;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> userId;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String number;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Date createtime;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String note;

    </span><span style="color: rgba(0, 0, 255, 1)">private</span> List&lt;OrdersDetail&gt; orderdetails;  <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">  一对多关系设置</span>


    }
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)"> OrdersDetail {
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> id;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> ordersId;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> itemsId;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> itemsNum;

}</span></pre>

OrdersMapper.java

package com.dx.mybatis01.dao;
import java.util.List;
import com.dx.mybatis01.model.Orders;
public interface OrdersMapper {
// 查询订单 (关联用户) 订单明细
public List<Orders> findOrderAndDetailResultMap();
}

OrdersMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dx.mybatis01.dao.OrdersMapper">
    <resultMap type="com.dx.mybatis01.model.Orders" id="OrderAndDetailResultMap">
        <!-- 配置映射的订单信息 -->
        <id column="id" property="id" />
        <result column="user_id" property="userId" />
        <result column="number" property="number" />
        <result column="createtime" property="createtime" />
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 配置关联的用户信息 association:用来映射关联查询单个对象的信息 一对多的逆向使用 property ：将关联信息映射到Order的哪个属性中去 
        javaType 映射到那个java类中 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">association </span><span style="color: rgba(255, 0, 0, 1)">property</span><span style="color: rgba(0, 0, 255, 1)">="user"</span><span style="color: rgba(255, 0, 0, 1)"> javaType</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.model.User"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)">  id 关联查询用户的唯一标识 ，外键 column 指定唯一标识用户信息的列  </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">id </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="id"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="username"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="username"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="gender"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="gender"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="address"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="address"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">association</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 订单明细信息 一个订单包含多条明细，要使用collection进行映射 一对多使用 配置在一的一方添加属性 collection：对关联查询的多条记录映射到集合对象中去 
        property: 将关联查询出来的多条记录映射到类中的那个属性中 list ofType : 指定映射到集合属性中的pojo类，list的泛型 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">collection </span><span style="color: rgba(255, 0, 0, 1)">property</span><span style="color: rgba(0, 0, 255, 1)">="orderdetails"</span><span style="color: rgba(255, 0, 0, 1)"> ofType</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.model.OrdersDetail"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> id 订单明细唯一标识 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">id </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="ordersdetail_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="id"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="itemsId"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_num"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="itemsNum"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="orders_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="ordersId"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">collection</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">resultMap</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

<span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">select </span><span style="color: rgba(255, 0, 0, 1)">id</span><span style="color: rgba(0, 0, 255, 1)">="findOrderAndDetailResultMap"</span><span style="color: rgba(255, 0, 0, 1)"> resultMap</span><span style="color: rgba(0, 0, 255, 1)">="OrderAndDetailResultMap"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span><span style="color: rgba(0, 0, 0, 1)">
    SELECT
        t10.id,t10.user_id,t10.number,t10.createtime,
        t11.username,t11.gender,t11.address,
        t12.ordersdetail_id,t12.items_id,t12.items_num,t12.orders_id
    FROM orders  t10
    inner join USER t11 on t10.user_id=t11.id
    left outer join ordersdetail t12 on t10.id=t12.orders_id
</span><span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">select</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

</mapper>

或者

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dx.mybatis01.dao.OrdersMapper">
    <resultMap id="BaseResultMap" type="com.dx.mybatis01.model.Orders">
        <id column="id" jdbcType="INTEGER" property="id" />
        <result column="user_id" jdbcType="INTEGER" property="userId" />
        <result column="number" jdbcType="INTEGER" property="number" />
        <result column="createtime" jdbcType="DATE" property="createtime" />
    </resultMap>
    <sql id="Base_Column_List">
        id, user_id, number, createtime
    </sql>
    <!-- 订单查询关联用户的查询 -->
    <resultMap type="com.dx.mybatis01.model.Orders" id="OrderUserResultMap"
        extends="BaseResultMap">
        <!-- 配置关联的用户信息 association: 用来映射关联查询单个对象的信息 property ：将关联信息映射到 Order 的哪个属性中去 
            javaType 映射到那个 java 类中 -->
        <association property="user" javaType="com.dx.mybatis01.model.User">
            <!-- id 关联查询用户的唯一标识 ，外键 column 指定唯一标识用户信息的字段，property 表示类中属性 -->
            <id column="id" property="id" />
            <result column="username" property="username" />
            <result column="gender" property="gender" />
            <result column="address" property="address" />
        </association>
    </resultMap>
<span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">resultMap </span><span style="color: rgba(255, 0, 0, 1)">type</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.model.Orders"</span><span style="color: rgba(255, 0, 0, 1)"> id</span><span style="color: rgba(0, 0, 255, 1)">="OrderAndDetailResultMap"</span><span style="color: rgba(255, 0, 0, 1)">
    extends</span><span style="color: rgba(0, 0, 255, 1)">="OrderUserResultMap"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 订单明细信息 一个订单包含多条明细，要使用collection进行映射 一对多使用 配置在一的一方添加属性 collection：对关联查询的多条记录映射到集合对象中去 
        property: 将关联查询出来的多条记录映射到类中的那个属性中 list ofType : 指定映射到集合属性中的pojo类，list的泛型 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">collection </span><span style="color: rgba(255, 0, 0, 1)">property</span><span style="color: rgba(0, 0, 255, 1)">="orderdetails"</span><span style="color: rgba(255, 0, 0, 1)"> ofType</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.model.OrdersDetail"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> id 订单明细唯一标识 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">id </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="ordersdetail_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="id"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="itemsId"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_num"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="itemsNum"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="orders_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="ordersId"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">collection</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">resultMap</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

<span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">select </span><span style="color: rgba(255, 0, 0, 1)">id</span><span style="color: rgba(0, 0, 255, 1)">="findOrderAndDetailResultMap"</span><span style="color: rgba(255, 0, 0, 1)"> resultMap</span><span style="color: rgba(0, 0, 255, 1)">="OrderAndDetailResultMap"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span><span style="color: rgba(0, 0, 0, 1)">
    SELECT
        t10.id,t10.user_id,t10.number,t10.createtime,
        t11.username,t11.gender,t11.address,
        t12.ordersdetail_id,t12.items_id,t12.items_num,t12.orders_id
    FROM orders t10
    inner join USER t11 on t10.user_id=t11.id
    left outer join ordersdetail t12 on t10.id=t12.orders_id
</span><span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">select</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

</mapper>

测试代码：

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.dx.mybatis01.dao.OrdersMapper;
import com.dx.mybatis01.model.Orders;
import com.dx.mybatis01.model.OrdersDetail;
public class OrdersMapperTest {
private SqlSessionFactory sqlSessionFactory = null;
private SqlSession session = null;
@Before
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> Init() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> IOException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 加载总配置文件，转化为流</span>
    String resource = "mybatis.cfg.xml"<span style="color: rgba(0, 0, 0, 1)">;
    InputStream inputStream </span>=<span style="color: rgba(0, 0, 0, 1)"> Resources.getResourceAsStream(resource);

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建sqlSessionFactory</span>
    sqlSessionFactory = <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactoryBuilder().build(inputStream);
    session </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
}

@After
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> destory() {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.session.close();
}

@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> test() {
    OrdersMapper ordersExtendsMapper </span>= session.getMapper(OrdersMapper.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
    List</span>&lt;Orders&gt; list =<span style="color: rgba(0, 0, 0, 1)"> ordersExtendsMapper.findOrderAndDetailResultMap();
    </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)"> (Orders o : list) {
        System.out.println(o.getId() </span>+ ":" + o.getUserId() + ":" + o.getUser().getUsername() + ":"
                + o.getUser().getAddress() + ":o.getOrderdetails().size()=" +<span style="color: rgba(0, 0, 0, 1)"> o.getOrderdetails().size());
        </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)"> (OrdersDetail od : o.getOrderdetails()) {
            System.out.println(</span>"------" + od.getId() + ":" + od.getItemsId() + ":" +<span style="color: rgba(0, 0, 0, 1)"> od.getItemsNum()
                    </span>+ ":" +<span style="color: rgba(0, 0, 0, 1)"> od.getOrdersId());
        }
    }
}

}

添加 log4j.properties 配置，设置打印执行 sql，在 Maven Module 项目 mybatis-relation 中 src/main/resources 下添加 log4j.properties

log4j.rootLogger=debug,stdout,logfile
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout
log4j.logger.com.ibatis=DEBUG
log4j.logger.com.ibatis.common.jdbc.SimpleDataSource=DEBUG
log4j.logger.com.ibatis.common.jdbc.ScriptRunner=DEBUG
log4j.logger.com.ibatis.sqlmap.engine.impl.SqlMapClientDelegate=DEBUG
log4j.logger.Java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

打印执行结果：

log4j:ERROR Could not find value for key log4j.appender.logfile
log4j:ERROR Could not instantiate appender named "logfile".
DEBUG - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - Opening JDBC Connection
Sun Mar 24 17:10:10 CST 2019 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
DEBUG - Created connection 1295083508.
DEBUG - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@4d3167f4]
DEBUG - ==>  Preparing: 
SELECT 
　　t10.id,t10.user_id,t10.number,t10.createtime, t11.username,t11.gender,t11.address, t12.ordersdetail_id,t12.items_id,t12.items_num,t12.orders_id 
FROM orders t10 inner 
join USER t11 on t10.user_id=t11.id 
left outer join ordersdetail t12 on t10.id=t12.orders_id 
DEBUG - ==> Parameters: 
DEBUG - <==      Total: 5
1:1:zhangsan: 北京市海淀区海淀黄庄:o.getOrderdetails().size()=2
------1:1:1:1
------2:2:1:1
2:2:lili: 北京市朝阳区大运村:o.getOrderdetails().size()=1
------3:1:1:2
3:2:lili: 北京市朝阳区大运村:o.getOrderdetails().size()=2
------4:2:1:3
------5:3:1:3
DEBUG - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@4d3167f4]
DEBUG - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@4d3167f4]
DEBUG - Returned connection 1295083508 to pool.

注意：

对于一对多或者多对一的查询，建议使用 ResultMap 映射进行代码编写，
mybatis 使用 resultMap 的 collection 对关联查询的多条记录映射到一个 list 集合属性中。

使用 resultType 实现：
将订单明细映射到 orders 中的 orderdetails 中，需要自己处理，使用双重循环遍历，去掉重复记录，将订单明细放在 orderdetails 中。
特别注意：

如果上边 ordersdetail 的唯一键数据库列名字为 id，则会导致 order 关联出来 ordersdetail 记录只为一条记录。

多对多查询

实例：查询用户及用户购买商品信息。
查询主表是：user
关联表：由于用户和商品没有直接关联，通过订单和订单明细进行关联，所以关联表：
orders、orderdetail、items
联结查询：内联结

利用 ResultMap

POJO 类

    public class User {
        private int id;
        private String username;
        private Date birthday;
        private String address;
        private String sex;
        private List<Orders> orderslist;    //一对多
    }
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)"> Orders {
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> User user;      <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 用户信息</span>
    <span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> id;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> userId;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String number;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Date createtime;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String note;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> List&lt;OrdersDetail&gt; orderdetails;    <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">商品信息存放集合</span>

    }
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)"> OrdersDetail {
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> id;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> ordersId;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> itemsId;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> itemsNum;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> Items items;    <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">商品信息</span>

    }
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)"> Items {
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> id;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String name;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">double</span><span style="color: rgba(0, 0, 0, 1)"> price;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String detail;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String pic;
    </span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Date createtime;
}</span></pre>

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dx.mybatis01.dao.UserMapper">   
    <!-- 用户及用户购买的商品明细 -->
    <resultMap type="com.dx.mybatis01.model.User" id="UserAndItemResultMap">
        <!-- 映射用户信息 -->
        <id column="user_id" property="id" />
        <result column="username" property="username" />
        <result column="gender" property="gender" />
        <result column="address" property="address" />
    <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 订单信息 一个用户创建多个订单 使用collection </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">collection </span><span style="color: rgba(255, 0, 0, 1)">property</span><span style="color: rgba(0, 0, 255, 1)">="orderslist"</span><span style="color: rgba(255, 0, 0, 1)"> ofType</span><span style="color: rgba(0, 0, 255, 1)">="com.dx.mybatis01.model.Orders"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">id </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="id"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="user_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="userId"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="number"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="number"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="createtime"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="createtime"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>

        <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 订单明细 一个订单包含多个订单明细 所以写在订单信息里面 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>

        <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">collection </span><span style="color: rgba(255, 0, 0, 1)">property</span><span style="color: rgba(0, 0, 255, 1)">="orderdetails"</span><span style="color: rgba(255, 0, 0, 1)"> ofType</span><span style="color: rgba(0, 0, 255, 1)">="com.wf.model.OrdersDetail"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
            <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> id 订单明细唯一标识 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">id </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="orderdetail_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="id"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="itemsId"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_num"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="itemsNum"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="orders_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="ordersId"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>

            <span style="color: rgba(0, 128, 0, 1)">&lt;!--</span><span style="color: rgba(0, 128, 0, 1)"> 商品信息 一个订单明细对应一个商品 </span><span style="color: rgba(0, 128, 0, 1)">--&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">association </span><span style="color: rgba(255, 0, 0, 1)">property</span><span style="color: rgba(0, 0, 255, 1)">="items"</span><span style="color: rgba(255, 0, 0, 1)"> javaType</span><span style="color: rgba(0, 0, 255, 1)">="com.wf.model.Items"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">id </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_id"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="id"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="items_name"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="name"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="item_price"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="price"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
                <span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">result </span><span style="color: rgba(255, 0, 0, 1)">column</span><span style="color: rgba(0, 0, 255, 1)">="item_datail"</span><span style="color: rgba(255, 0, 0, 1)"> property</span><span style="color: rgba(0, 0, 255, 1)">="detail"</span> <span style="color: rgba(0, 0, 255, 1)">/&gt;</span>
            <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">association</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
        <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">collection</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
    <span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">collection</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">resultMap</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>
<span style="color: rgba(0, 0, 255, 1)">&lt;</span><span style="color: rgba(128, 0, 0, 1)">select </span><span style="color: rgba(255, 0, 0, 1)">id</span><span style="color: rgba(0, 0, 255, 1)">="findUserAndItemResultMap"</span><span style="color: rgba(255, 0, 0, 1)"> resultMap</span><span style="color: rgba(0, 0, 255, 1)">="UserAndItemResultMap"</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span><span style="color: rgba(0, 0, 0, 1)">
    select
     t10.*,t11.*,t12.*,t13.*
    from user t10
    left outer join orders t11 on t10.user_id=t11.id
    left outer join ordersdetail t12 on t11.id=t12.order_id
    left outer join items t13 on t12.items_id=t13.items_id
    where id = #{id,jdbcType=INTEGER}
</span><span style="color: rgba(0, 0, 255, 1)">&lt;/</span><span style="color: rgba(128, 0, 0, 1)">select</span><span style="color: rgba(0, 0, 255, 1)">&gt;</span>

</mapper>

注意：

这里是把 user 的 id 修改为了 user_id，否则也会造成上边提到的错误，导致关联出来订单不是多条只能是一条。

参考：

https://blog.csdn.net/sinat_28978689/article/details/74999738

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MyBatis(五)：mybatis关联映射

创建数据 Demo 表

数据库表：

数据模型：

数据表之间的关系：

创建 Demo 表

配置 mybatis-generator 插件，生成 mapper、mapper.xml、model 代码:

一对一查询

利用 ResultType

利用 ResultMap

一对多查询

利用 ResultMap

多对多查询

利用 ResultMap

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MyBatis(五)：mybatis关联映射