10.多对一处理

10.多对一处理

测试环境搭建

1. 导入lombok

   <dependencies>
   	<!--Lombok-->
   	<dependency>
   		<groupId>org.projectlombok</groupId>
   		<artifactId>lombok</artifactId>
   		<version>1.18.10</version>
   	</dependency>
   </dependencies>
   

2. 新建实体类teacher和student

   package com.believe.pojo;
   
   import lombok.Data;
   
   @Data
   public class Teacher {
       private int id;
       private String name;
   }
   

   package com.believe.pojo;
   
   import lombok.Data;
   
   @Data
   public class Student {
       private int id;
       private String name;
       private Teacher teacher;
   }
   

3. 新建Mapper接口

   package com.believe.mapper;
   
   public interface TeacherMapper {
   }
   

   package com.believe.mapper;
   
   public interface StudentMapper {
   }
   

4. 新建Mapper.xml文件

   <?xml version="1.0" encoding="UTF-8" ?>
   <!DOCTYPE mapper
           PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
           "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
   
   <mapper namespace="com.believe.mapper.TeacherMapper">
   
   </mapper>
   

   <?xml version="1.0" encoding="UTF-8" ?>
   <!DOCTYPE mapper
           PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
           "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
   
   <mapper namespace="com.believe.mapper.StudentMapper">
   
   </mapper>
   

5. 在mybatis-config绑定Mapper.xml

   <!--绑定接口-->
   <mappers>
       <mapper resource="com/believe/mapper/StudentMapper.xml"/>
       <mapper resource="com/believe/mapper/TeacherMapper.xml"/>
   </mappers>
   

6. 测试

SQL语句

select s.id,s.name,t.name from student s,teacher t where s.tid = t.id;

按照查询嵌套处理

<select id="getStudent01" resultMap="getStudent01" >
	select * from student;
</select>
<resultMap id="getStudent01" type="student">
    <result property="id" column="id" />
    <result property="name" column="name" />
    <association property="teacher" column="tid" javaType="Teacher" select="getTeacher01" />
</resultMap>
<select id="getTeacher01" resultType="Teacher" >
	select * from teacher where id = #{tid};
</select>

按照结果嵌套处理

<select id="getStudent02" resultMap="getStudent02" >
	select s.id sid,s.name sname,t.id tid,t.name tname from student s,teacher t where s.tid = t.id;
</select>
<resultMap id="getStudent02" type="student" >
    <result property="id" column="sid" />
    <result property="name" column="sname" />
    <association property="teacher" javaType="Teacher"  >
        <result property="id" column="tid" />
        <result property="name" column="tname" />
    </association>
</resultMap>

原文地址：https://www.cnblogs.com/thetree/p/10_mybatis.html