技術標籤：ssmmybatis

mybatis多表聯合查詢（單一物件）

只需要一個StudentMapper（一條SQL聯合查詢）就夠

• Student為學生類，每個學生有自己的老師編號（tid），Teacher老師類，編號id
• 現在通過s.tid=t.id將兩張表聯合
• association的寫法和N+1有區別

<?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="cn.wit.mapper.StudentMapper">
	<resultMap type="Student" id="stuMap1">
		<id column="sid" property="id"/>
		<result column="sname" property="name"/>
		<result column="age" property
 
="age"/>
		<result column="tid" property="tid"/>
		
		<association property="teacher" javaType="Teacher" >
			<id column="tid" property="id"/>
			<result column="tname" property="name"/>
		</
 
association>
	</resultMap>
	
	<select id="selAll1" resultMap="stuMap1"> 
		select s.id sid,s.name sname,age age,t.id
		tid,t.name tname FROM student s left outer join teacher t on s.tid=t.id
	</select>
</mapper>

mybatis多表聯合查詢（物件集合）

cn.wit.pojo

Student

• id
• name
• age
• tid

Teacher

• id
• name
• List<?>

StudentMapper.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="cn.wit.mapper.TeacherMapper">

	<resultMap type="teacher" id="mymap">
		<id column="id" property="id"/>
		<result column="name" property="name"/>
		<collection property="list" ofType="student">
			<id column="sid" property="id"/>
			<result column="sname" property="name"/>
			<result column="age" property="age"/>
			<result column="tid" property="tid"/>
		</collection>
	</resultMap>
	<select id="selAll" resultMap="mymap">
		select t.id id,t.name name,
		s.id sid,s.name sname,age,tid  FROM teacher t left outer join student s on s.tid=t.id 
	</select>
</mapper>