技術標籤：ssmmybatis

resultMap 實現單表對映關係

去掉了resultType（auto_Mapping），替換成resultMap

• type為對映的類
• id標籤為主鍵
• result為其他列
• column表示列名
• property表示對應的屬性名

<resultMap type="Teacher" id="mybatis">
		<id column="id" property="id"/>
		<result column="name" property
 
="name"/>
	</resultMap>
	<select id="selById" parameterType="int" resultMap="mybatis">
		select * from teacher where id=#{0}

resultMap多表查詢(單一物件)

• 與業務裝配方式的區別：student中teacher的賦值書寫位置改變
• 前 serviceImpl: student.setTeacher(mapper.selById(student.getId()))
• 後 StudentMapper.xml
  利用association標籤通過tid呼叫cn.wit.mapper.selById將teacher對映過來
• 大前提:使用 N+1 方式時,如果列名和屬性名相同可以不配置,使用 Auto mapping 特性.但是 mybatis 預設只會給列專配一次(association中傳遞了tid，tid就必須要配置一遍)

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.StudentMapper">
	<resultMap type="student" id="mybatis">
		<id column="id" property="id"/>
		<result column="name" property="name"/>
		<result column="age" property="age"/>
		<result column="tid" property="tid"/>
		<association property="teacher"  select="cn.wit.mapper.TeacherMapper.selById" column="tid"></association>
		
	</resultMap>
	<select id="selByPage" parameterType="pageinfo" resultMap="mybatis">
		select * from student limit #{pageStart},#{pageSize}
	</select>
	
	<select id="selCountByPageInfo" resultType="long" >
		select count(*) from student 
	</select>
</mapper>

TeacherMapper.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">
	<select id="selById" parameterType="int" resultType="teacher">
		select * from teacher where id=#{0}
	</select>
</mapper>

mybatis多表查詢（物件集合）

cn.wit.pojo

Student

• id
• name
• age
• tid

Teacher

• id
• name
• List<?>

cn.wit.mapper

StudentMapper(interface)

TeacherMapper（interface）

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.StudentMapper">
	<select id="selById" resultType="Student" parameterType="int">
		select *from student where tid=#{0}
	</select>
</mapper>

TeacherMapper.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" select="cn.wit.mapper.StudentMapper.selById" column="id"></collection>
	</resultMap>
	<select id="selAll" resultMap="mymap">
		select *from teacher 
	</select>
</mapper>

cn.wit.Test

public class Test {
	public static void main(String[] args) {
		SqlSession session = MyBatisUtil.getSession();
		TeacherMapper mapper = session.getMapper(TeacherMapper.class);
		List<Teacher> list = mapper.selAll();
		for (Teacher teacher : list) {
			System.out.println(teacher);
		}
	}
}

總結

• 單一物件和物件集合resultMap使用區別
• 單一物件使用association標籤 屬性為javaType
• 物件集合使用collection標籤 屬性為ofType