平時在開發過程中dao、bean和XML檔案都是自動生成的，很少寫XML的配置關係，今天記錄一下mybatis的關聯查詢中的多對一和一對多的情況。

首先是有兩張表(學生表Student和老師Teacher表，注：這裡只是為了演示一對多和多對一的情況，請不要槓)，為了更易懂，這裡只設置了最簡單的幾個必要欄位。表結構如下圖

Student表：

Teacher表：

建立實體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
} 

下面重點來了：配置Mapper.xml檔案：

<?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"> 
 
 <!-- ///一對多的第一種寫法/// -->
 <resultMap type="Teacher" id="teacherMap">
  <id column="id" property="id"/>
  <result column="name" property="name"/>
   <collection property="students" ofType="Student" column="id">
    <!-- 這裡的column對應的是下面查詢的別名，而不是表字段名 -->
  <id column="sid" property="id"/>
    <!-- property對應JavaBean中的屬性名 -->
  <result column="sname" property="name"/>
  <result column="className" property="className"/>
  </collection>
 </resultMap>
 
 
 <!-- 查詢所有的老師級各自的所有學生 -->
 <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>

測試類：

package com.tz.test;

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.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);
 }
 
}

下面給出第二種寫法：

<!-- //一對多的第二種寫法/ -->
 <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>
 
 
 <!-- 查詢所有的老師級各自的所有學生 -->
 <select id="getAllTeacher" parameterType="Teacher" resultMap="teacherMaps">
 SELECT
 t.id,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>

測試類：

@Test
 public void getTeachers2() {
 SqlSession session = sqlSessionFactory.openSession();
 List<Teacher> list = session.selectList("com.tz.mybatis.dao.studentDao.getAllTeacher");
 System.out.println(list);
 }

查詢學生資訊(多對一)：

首先還是配置檔案：

<resultMap type="Student" id="studentMap">
 <id column="id" property="id"/>
 <result column="name" property="name"/>
 <result column="class_name" property="className"/>
 <result column="teacher_id" property="teacherId"/>
 <association property="teacher" select="getTeacher" column="teacher_id" javaType="Teacher">
 <!-- 這裡要注意的是column對應的是student中的外來鍵，而且需是表字段名 -->
 </association>
 </resultMap>
 
 
 <select id="getStudent" resultMap="studentMap">
 SELECT
 s.id,s.name,s.class_name,s.teacher_id
 FROM
 student s
 </select>
 
 <select id="getTeacher" resultType="Teacher" parameterType="int">
 SELECT
 t.id,t.name,t.class_name as className 
 FROM teacher t 
 where id = #{teacher_id}
 </select>

測試類：

@Test
 public void getStudents() {
 SqlSession session = sqlSessionFactory.openSession();
 List<Student> list = session.selectList("com.tz.mybatis.dao.studentDao.getStudent");
 System.out.println(list);
 }

最後：當然如果不想配置這麼麻煩的資訊，可以直接寫一個關聯查詢的SQL語句，返回結果直接由Map接受即可。不過這樣就不太符合面向物件的理念了。

到此這篇關於Mybatis關聯查詢之一對多和多對一XML配置詳解的文章就介紹到這了,更多相關Mybatis關聯查詢內容請搜尋我們以前的文章或繼續瀏覽下面的相關文章希望大家以後多多支援我們！