平时在开发过程中dao、bean和XML文件都是自动生成的，很少写XML的配置关系，今天记录一下mybatis的关联查询中的多对一和一对多的情况。
首先是有两张表(学生表Student和老师Teacher表，注：这里只是为了演示一对多和多对一的情况，请不要杠)，为了更易懂，这里只设置了最简单的几个必要字段。表结构如下图
Student表：
Teacher表：
创建实体bean
Teacher.java:
import java.util.List;
public class Teacher {
private Integer id;
private String name;
private String className;
private List<Student> students;
// get、set方法省略
}
Sfudent.java
public class Student {
private Integer id;
private String name;
private Integer teacherId;
private String className;
private Teacher teacher;
// get、set方法省略
}
下面重点来了：配置Mapper.xml文件：
<?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.tz.mybatis.dao.studentDao">
<!-- ///一对多的第一种写法/// -->
<resultMap type="Teacher" id="teacherMap">
<id column="id" property="id"/>
<result column="name" property="name"/>
<collection property="students" ofType="Student" column="id">
<!-- 这里的column对应的是下面查询的别名，而不是表字段名 -->
<id column="sid" property="id"/>
<!-- property对应JavaBean中的属性名 -->
<result column="sname" property="name"/>
<result column="className" property="className"/>
</collection>
</resultMap>
<!-- 查询所有的老师级各自的所有学生 -->
<select id="getTeachers" parameterType="Teacher" resultMap="teacherMap">
SELECT
t.id,
t.NAME,
t.class_Name,
s.id AS sid,
s. NAME AS sname,
s.class_name as className
FROM
teacher t
LEFT JOIN student s ON t.id = s.teacher_id
</select>
</mapper>
测试类：
package com.tz.test;
import java.io.IOException;
<em>本文来源gao.dai.ma.com搞@代*码(网$</em>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.Before;
import org.junit.Test;
import com.tz.mybatis.bean.Student;
import com.tz.mybatis.bean.Teacher;
public class TeacherTest {
private SqlSessionFactory sqlSessionFactory;
@Before
public void init() throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
public void getTeachers() {
SqlSession session = sqlSessionFactory.openSession();
List<Teacher> list = session.selectList("com.tz.mybatis.dao.studentDao.getTeachers");
System.out.println(list);
}
}
下面给出第二种写法：
<!-- //一对多的第二种写法/ -->
<resultMap type="Teacher" id="teacherMaps">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="class_name" property="className"/>
<collection property="students" ofType="Student" select="getStudents" column="id">
</collection>
</resultMap>
<!-- 查询所有的老师级各自的所有学生 -->
<select id="getAllTeacher" parameterType="Teacher" resultMap="teacherMaps">
SELECT
t.id,
t.NAME,
t.class_name
FROM
teacher t
</select>
<select id="getStudents" parameterType="int" resultType="Student">
select
s.id,
s. NAME,
s.class_name as className
from student s
where teacher_id = #{id}
</select>
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转载请注明原文链接：Mybatis关联查询之一对多和多对一XML配置详解
转载请注明原文链接：Mybatis关联查询之一对多和多对一XML配置详解
