Mybatis第四讲——关联一对一（2）

Mybatis第三讲——关联一对一（一）

本讲讲述另一种关联一对一的映射方法，这种是推荐使用的最常用的方法。

工程目录:

与前一讲相比，增加了AddressMapper.java 和AddressMapper.xml两个文件：

AddressMapper.java:

package com.java1234.mappers;

import com.java1234.model.Address;

public interface AddressMapper {
	public Address findAddressById(Integer id);
}

AddressMapper.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="com.java1234.mappers.AddressMapper">
	
	<resultMap type="Address" id="addressResult">
	 	<result property="id" column="id"/>
		<result property="sheng" column="sheng"/>
		<result property="shi" column="shi"/>
		<result property="qu" column="qu"/> 
	</resultMap>
	
<select id="findAddressById" resultMap="addressResult">
select * from t_address where id=#{id}
</select>
</mapper> 

StudentMapper.java中内容没变：

package com.java1234.mappers;

import java.util.List;

import com.java1234.model.Student;

public interface StudentMapper {

	public int add(Student student);
	public int delete(Integer id);
	public int update(Student student);
	public Student getStudentById(Integer id);
	public List<Student> getAllStudents();
	public Student findStudentWithAddress(Integer id);
}

StudentMapper.xml中内容修正如下：

<?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.java1234.mappers.StudentMapper">

	<insert id="add" parameterType="Student"  >
		insert into t_student values(null,#{name},#{age})
	</insert>
	
	<delete id="delete" parameterType="Integer">
	 delete from t_student where id=#{id}
	</delete>
	
	<update id="update" parameterType="Student">
	update t_student set name=#{name},age=#{age} where id=#{id}
	</update>
	
	<select id="getStudentById" parameterType="Integer" resultType="Student">
	select * from t_student where id=#{id}
	</select>

	
	
	
	
	<resultMap type="Student" id="StudentResult">
		<id property="id" column="id"/>
		<result property="name" column="name"/>
		<result property="age" column="age"/>
		
		<association property="address" column="addressId" select="com.java1234.mappers.AddressMapper.findAddressById"/>
	</resultMap> 
	
	<select id="getAllStudents" resultMap="StudentResult">
	select * from t_student 
	</select>
	
	<select id="findStudentWithAddress" resultMap="StudentResult" parameterType="Integer">
	select * from t_student t1,t_address t2 where t1.addressId=t2.id and t2.id=#{id} 
	</select>
</mapper> 

其中<association property="address" column="addressId" select="com.java1234.mappers.AddressMapper.findAddressById"/>里面的

column=“addressId”中的“addressId“是t_student表中的字段addressId，属于逻辑意义上的外键，对应于t_address表中的主键“id”。

 测试：

结果：