Mybatis第四讲——关联一对一（2）

小鱼儿 2022-03-17 16:17 219阅读 0赞

[Mybatis第三讲——关联一对一（一）][Mybatis]

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:

![20190225111435813.png][]

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：

![20190225112139376.png][]

结果：

![20190225112150738.png][]

[Mybatis]: https://blog.csdn.net/yongbutingxide/article/details/87911613
[20190225111435813.png]: /images/20220317/9a606d0f4f76468c809ddc0acb03c5d7.png
[20190225112139376.png]: /images/20220317/31a9696e38884dcc8fc2be17ba7e64b8.png
[20190225112150738.png]: /images/20220317/3906d4e5316d4114a3a89e4e58249801.png