"学习过 Hibernate 框架的伙伴们很容易就能简单的配置各种映射关系 (Hibernate 框架的映射关系在我的 blogs 中也有详细的讲解)，但是在 Mybatis 框架中我们又如何去实现一对多的关系映射呢？其实很简单首先我们照常先准备前期的环境 (具体解释请参考初识 Mybatis ...."

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Mybatis框架中实现双向一对多关系映射

学习过 Hibernate 框架的伙伴们很容易就能简单的配置各种映射关系 (Hibernate 框架的映射关系在我的 blogs 中也有详细的讲解)，但是在 Mybatis 框架中我们又如何去实现

一对多的关系映射呢？其实很简单

首先我们照常先准备前期的环境 (具体解释请参考初识 Mybatis 进行增、删、改、查 blogs) 这里我就直接上代码了

主配置文件：Configuration.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>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC">
<property name="" value=""/>
</transactionManager>
<dataSource type="UNPOOLED">
<property name="driver" value="oracle.jdbc.OracleDriver"/>
<property name="url" value="jdbc:oracle:thin:@localhost:1521:orcl"/>
<property name="username" value="practice"/>
<property name="password" value="123"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="config/Student.xml"/>
<mapper resource="config/Grade.xml"/>
</mappers>
</configuration>

背景：学生和班级是一个典型的一对多的关系，一个班级可以对应着多个学生，所以我们随即创建了学生对象和班级对象

学生类：Student

package entity;
/*
 * 学生类
 * */
public class Student {
    //学生编号
    private Integer sid;
    //学生名称
    private String sname;
    //学生性别
    private String sex;
</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Student() {
}
</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Student(String sname, String sex) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.sname =<span style="color: rgba(0, 0, 0, 1)"> sname;
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.sex =<span style="color: rgba(0, 0, 0, 1)"> sex;
}
</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Integer getSid() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> sid;
}
</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)"> setSid(Integer sid) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.sid =<span style="color: rgba(0, 0, 0, 1)"> sid;
}
</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> String getSname() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> sname;
}
</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)"> setSname(String sname) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.sname =<span style="color: rgba(0, 0, 0, 1)"> sname;
}
</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> String getSex() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> sex;
}
</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)"> setSex(String sex) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.sex =<span style="color: rgba(0, 0, 0, 1)"> sex;
}

}

班级类：Grade

package entity;
import java.util.HashSet;
import java.util.Set;
/*


班级类


*/
public class Grade {
//班级编号
private Integer gid;
//班级名称
private String gname;
//班级描述
private String gdesc;
//班级下的学生信息
private Set<Student> stus=new HashSet<Student>();
public Set<Student> getStus() {
return stus;
}
public void setStus(Set<Student> stus) {
this.stus = stus;
}
public Grade() {
}
public Grade(Integer gid, String gname, String gdesc) {
this.gid = gid;
this.gname = gname;
this.gdesc = gdesc;
}
public Integer getGid() {
return gid;
}
public void setGid(Integer gid) {
this.gid = gid;
}
public String getGname() {
return gname;
}
public void setGname(String gname) {
this.gname = gname;
}
public String getGdesc() {
return gdesc;
}
public void setGdesc(String gdesc) {
this.gdesc = gdesc;
}


}

实体类准备完了的话，我们就可以开始看配置文件了，也是最关键的一部分

首先讲简单点的学生实体类对应的配置文件

Student.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="Student">
<resultMap type="entity.Student" id="StudentResult">
<id column="sid" jdbcType="INTEGER" property="sid"/>
<result column="sname" jdbcType="VARCHAR" property="sname"/>
<result column="sex" jdbcType="VARCHAR" property="sex"/>
</resultMap>
</mapper>

然后就是最关键的班级实体的配置文件了

Grade.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="Grade">
<resultMap type="entity.Grade" id="GradeResult">
<id column="gid" jdbcType="INTEGER" property="gid"/>
<result column="gname" jdbcType="VARCHAR" property="gname"/>
<result column="gdesc" jdbcType="VARCHAR" property="gdesc"/>
<!-- 一对多关系 -->
<collection property="stus" resultMap="Student.StudentResult"></collection>
</resultMap>
&lt;!-- 查询所有信息 --&gt;
&lt;<span style="color: rgba(0, 0, 255, 1)">select</span> id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">selectAllInfo</span><span style="color: rgba(128, 0, 0, 1)">"</span> resultMap=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">GradeResult</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;
    &lt;!-- <span style="color: rgba(0, 0, 255, 1)">select</span> sid,sname,sex,g.gid,gname,gdesc <span style="color: rgba(0, 0, 255, 1)">from</span> Student s,Grade g <span style="color: rgba(0, 0, 255, 1)">where</span> s.gid=g.gid --&gt;
    <span style="color: rgba(0, 0, 255, 1)">select</span> sid,sname,sex,g.gid,gname,gdesc <span style="color: rgba(0, 0, 255, 1)">from</span> Student s left join Grade g on s.gid=<span style="color: rgba(0, 0, 0, 1)">g.gid
</span>&lt;/<span style="color: rgba(0, 0, 255, 1)">select</span>&gt;

</mapper>

以上就是对配置文件的解释了

接下来我们就可以进行一道测试了

/*
     * 1.1 查询所有的班级和班级下的所有学生 (一对多)
     * */
    @Test
    public void selectAllStu() throws Exception{
        //通过配置文件获取到数据库连接信息
        Reader reader = Resources.getResourceAsReader("config/Configuration.xml");
        //通过配置信息构建一个 SessionFactory 工厂
        SqlSessionFactory sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader);
        //通过 SessionFaction 打开一个回话通道
        SqlSession session = sqlsessionfactory.openSession();
        /*SqlSession session =MybatisUtil.getSession();*/
        //调用配置文件中的 sql 语句
        List<Grade> list = session.selectList("Grade.selectAllInfo");
        //遍历查询出来的结果
        for (Grade grade : list) {
            System.out.println("班级："+grade.getGname());
            for (Student stu : grade.getStus()) {
                System.out.println("学生："+stu.getSname());}
        }
    session.close();
}
</span></pre>

执行后，查询出来的结果是

以上是第一种一对多关系映射的方式，下面是第二种一对多映射的方法，其他的所有步骤和上面的都是一样的只有相对应的配置文件不同，所以我就只贴小配置了

Grade.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="Grade">
<resultMap type="entity.Grade" id="GradeResult">
<id column="gid" jdbcType="INTEGER" property="gid"/>
<result column="gname" jdbcType="VARCHAR" property="gname"/>
<result column="gdesc" jdbcType="VARCHAR" property="gdesc"/>
<!-- 一对多关系 -->
<!-- <collection property="stus" resultMap="Student.StudentResult"></collection>  -->
<collection property="stus" javaType="entity.Student">
<id property="sid" column="sid"/>
<result property="sname" column="sname"/>
<result property="sex" column="sex"/>
</collection>
</resultMap>
&lt;!-- 查询所有信息 --&gt;
&lt;<span style="color: rgba(0, 0, 255, 1)">select</span> id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">selectAllInfo</span><span style="color: rgba(128, 0, 0, 1)">"</span> resultMap=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">GradeResult</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;
    &lt;!-- <span style="color: rgba(0, 0, 255, 1)">select</span> sid,sname,sex,g.gid,gname,gdesc <span style="color: rgba(0, 0, 255, 1)">from</span> Student s,Grade g <span style="color: rgba(0, 0, 255, 1)">where</span> s.gid=g.gid --&gt;
    <span style="color: rgba(0, 0, 255, 1)">select</span> sid,sname,sex,g.gid,gname,gdesc <span style="color: rgba(0, 0, 255, 1)">from</span> Student s left join Grade g on s.gid=<span style="color: rgba(0, 0, 0, 1)">g.gid
</span>&lt;/<span style="color: rgba(0, 0, 255, 1)">select</span>&gt;

&lt;!-- 新增班级并同时新增班级下的学生 --&gt;
&lt;!--useGeneratedKeys=<span style="color: rgba(0, 0, 255, 1)">true</span><span style="color: rgba(0, 0, 0, 1)"> 表明采用主键生成策略
    keyProperty</span>=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">gid</span><span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(0, 0, 0, 1)">  表明将生成的主键添加到parameterType类中的那个属性值中去
  </span>--&gt;
&lt;!-- &lt;insert id=<span style="color: rgba(128, 0, 0, 1)">""</span> useGeneratedKeys=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">true</span><span style="color: rgba(128, 0, 0, 1)">"</span> keyProperty=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">gid</span><span style="color: rgba(128, 0, 0, 1)">"</span> parameterType=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">entity.Grade</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;
    
&lt;/insert&gt; --&gt;

</mapper>

接下来就可以在多的一方配置一的关联关系了

Student.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="Student">
<resultMap type="entity.Student" id="StudentResult">
<id column="sid" jdbcType="INTEGER" property="sid"/>
<result column="sname" jdbcType="VARCHAR" property="sname"/>
<result column="sex" jdbcType="VARCHAR" property="sex"/>
<!-- 多对一 -->
<!--  <association property="grade" resultMap="Grade.GradeResult"></association> -->
<association property="grade" javaType="entity.Grade">
<id property="gid" column="gid"/>
<result property="gname" column="gname"/>
<result property="gdesc" column="gdesc"/>
</association>
</resultMap>
&lt;!-- 使用别名 --&gt;
&lt;sql id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">cloums</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;<span style="color: rgba(0, 0, 0, 1)">
    s.sid,s.sname,s.sex ,g.gid,g.gname,g.gdesc
</span>&lt;/sql&gt;
&lt;!-- 多对一查询学生的班级 --&gt;
&lt;<span style="color: rgba(0, 0, 255, 1)">select</span> id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">selectGradeByStu</span><span style="color: rgba(128, 0, 0, 1)">"</span> resultMap=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">StudentResult</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;
    <span style="color: rgba(0, 0, 255, 1)">select</span> &lt;include refid=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">cloums</span><span style="color: rgba(128, 0, 0, 1)">"</span>/&gt; <span style="color: rgba(0, 0, 255, 1)">from</span> Student s ,Grade g <span style="color: rgba(0, 0, 255, 1)">where</span> s.gid=<span style="color: rgba(0, 0, 0, 1)">g.gid
</span>&lt;/<span style="color: rgba(0, 0, 255, 1)">select</span>&gt;

&lt;!-- 简单查询所有信息 --&gt;
 &lt;<span style="color: rgba(0, 0, 255, 1)">select</span> id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">selectAllStu</span><span style="color: rgba(128, 0, 0, 1)">"</span>  resultMap=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">StudentResult</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;
    <span style="color: rgba(0, 0, 255, 1)">select</span> sid,sname,sex,gid <span style="color: rgba(0, 0, 255, 1)">from</span><span style="color: rgba(0, 0, 0, 1)"> Student 
</span>&lt;/<span style="color: rgba(0, 0, 255, 1)">select</span>&gt; 

&lt;!--动态拼接Sql  --&gt;
 &lt;<span style="color: rgba(0, 0, 255, 1)">select</span> id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">selectAllStuByWhere</span><span style="color: rgba(128, 0, 0, 1)">"</span> parameterType=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">entity.Student</span><span style="color: rgba(128, 0, 0, 1)">"</span>  resultMap=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">StudentResult</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;
    <span style="color: rgba(0, 0, 255, 1)">select</span> sid,sname,sex,gid <span style="color: rgba(0, 0, 255, 1)">from</span> Student <span style="color: rgba(0, 0, 255, 1)">where</span> <span style="color: rgba(128, 0, 128, 1)">1</span>=<span style="color: rgba(128, 0, 128, 1)">1</span>
    &lt;<span style="color: rgba(0, 0, 255, 1)">if</span> test=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">sname!=null and !&amp;quot;&amp;quot;.equals(sname.trim())</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;
        &lt;!-- and sname like <span style="color: rgba(128, 0, 0, 1)">'</span><span style="color: rgba(128, 0, 0, 1)">%</span><span style="color: rgba(128, 0, 0, 1)">'</span>|| #{sname}|| <span style="color: rgba(128, 0, 0, 1)">'</span><span style="color: rgba(128, 0, 0, 1)">%</span><span style="color: rgba(128, 0, 0, 1)">'</span> --&gt; &lt;!-- 模糊查询 --&gt;<span style="color: rgba(0, 0, 0, 1)">
        and sname like </span><span style="color: rgba(128, 0, 0, 1)">'</span><span style="color: rgba(128, 0, 0, 1)">%${sname}%</span><span style="color: rgba(128, 0, 0, 1)">'</span>&lt;!-- 模糊查询 --&gt;
        &lt;!-- and sname = #{sname} --&gt;
    &lt;/<span style="color: rgba(0, 0, 255, 1)">if</span>&gt;
 &lt;/<span style="color: rgba(0, 0, 255, 1)">select</span>&gt;
 
 &lt;!-- 新增学生信息 --&gt;
 &lt;insert id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">InsertStuInfo</span><span style="color: rgba(128, 0, 0, 1)">"</span> parameterType=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">entity.Student</span><span style="color: rgba(128, 0, 0, 1)">"</span> &gt;<span style="color: rgba(0, 0, 0, 1)">
     insert into Student values(SEQ_NUM.Nextval,#{sname},#{sex},</span><span style="color: rgba(128, 0, 128, 1)">1</span><span style="color: rgba(0, 0, 0, 1)">)
 </span>&lt;/insert&gt;
 
 &lt;!-- 删除学生信息 --&gt;
 &lt;insert id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">DeleteStuBySid</span><span style="color: rgba(128, 0, 0, 1)">"</span> parameterType=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">int</span><span style="color: rgba(128, 0, 0, 1)">"</span>&gt;<span style="color: rgba(0, 0, 0, 1)">
     delete </span><span style="color: rgba(0, 0, 255, 1)">from</span> Student <span style="color: rgba(0, 0, 255, 1)">where</span> sid=<span style="color: rgba(0, 0, 0, 1)">#{sid}
 </span>&lt;!--或者是     delete <span style="color: rgba(0, 0, 255, 1)">from</span> Student <span style="color: rgba(0, 0, 255, 1)">where</span> sid=#{_parameter} --&gt;
 &lt;/insert&gt;
 
 &lt;!-- 根据SID修改学生信息 --&gt;
 &lt;update id=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">UpdateStuBySid</span><span style="color: rgba(128, 0, 0, 1)">"</span> parameterType=<span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">entity.Student</span><span style="color: rgba(128, 0, 0, 1)">"</span> &gt;<span style="color: rgba(0, 0, 0, 1)">
     update Student </span><span style="color: rgba(0, 0, 255, 1)">set</span> sname=#{sname},sex=#{sex} <span style="color: rgba(0, 0, 255, 1)">where</span> sid=<span style="color: rgba(0, 0, 0, 1)">#{sid}
 </span>&lt;/update&gt;

</mapper>

这样就已经完成了 Mybatis 框架中的简单的双向一对多的配置了，怎么样，是不是没有想象中的难呢？希望对大家有点帮助吧！

Mybatis框架中实现双向一对多关系映射

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Mybatis框架中实现双向一对多关系映射