MyBatis3一对一关系映射

1. MyBatis3关系映射，一对一关系

创建t_address表
create table t_address (
id int(11) NOT NULL AUTO_INCREMENT,
sheng varchar(20) DEFAULT NULL,
shi varchar(20) DEFAULT NULL,
qu varchar(20) DEFAULT NULL,
PRIMARY KEY(id)
) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;

插入数据
insert into t_address(id, sheng, shi, qu) values(1, '北京市', '北京市', '东城区');
insert into t_address(id, sheng, shi, qu) values(2, '河北省', '石家庄市', '新华区');

在t_student表增加addressId关联字段
alter table t_student add addressId INT(11);

如果使用外键(当前情况不需要)：
alter table t_student add FOREIGN KEY fk_student_address(addressId) REFERENCES t_address(id);
alter table t_student drop foreign key t_student_ibfk_1;
alter table t_student drop index fk_student_address;

2. 使用mybatis查询一对一关系关联表的方式

1. 不推荐
<resultMap type="Student" id="StudentAddressResult">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="age" column="age"/>
    <result property="address.id" column="addressId"/>
    <result property="address.sheng" column="sheng"/>
    <result property="address.shi" column="shi"/>
    <result property="address.qu" column="qu"/>
</resultMap>

2. 不推荐
<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>
<resultMap type="Student" id="StudentAddressResult">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="age" column="age"/>
    <association property="address" resultMap="AddressResult"/>
</resultMap>

3. 不推荐
<resultMap type="Student" id="StudentAddressResult">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="age" column="age"/>
    <association property="address" javaType="Address">
        <result property="id" column="id"/>
        <result property="sheng" column="sheng"/>
        <result property="shi" column="shi"/>
        <result property="qu" column="qu"/>
    </association>
</resultMap>

4. 推荐(column对应的是sql表中的外键)
StudentMapper.xml
<resultMap type="Student" id="StudentAddressResult">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="age" column="age"/>
    <association property="address" column="addressId" select="com.andrew.mappers.AddressMapper.findById"></association>
</resultMap>
AddressMapper.xml
<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="findById" parameterType="Integer" resultType="Address">
    select * from t_address where id=#{id}
</select>

3. 使用mybatis查询关联表

package com.andrew.model;
public class Address {
    private Integer id;
    private String sheng;
    private String shi;
    private String qu;
    @Override
    public String toString() {
        return "Address [id=" + id + ", sheng=" + sheng + ", shi=" + shi
                + ", qu=" + qu + "]";
    }
    // getter and setter
}

package com.andrew.model;
public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private Address address;
    public Student() {
        super();
    }
    public Student(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }
    public Student(Integer id, String name, Integer age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age
                + ", address=" + address + "]";
    }
    // getter and setter
}

package com.andrew.mappers;
import com.andrew.model.Address;
public interface AddressMapper {
    public Address findById(Integer id);
}

<?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.andrew.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="findById" parameterType="Integer" resultType="Address">
        select * from t_address where id=#{id}
    </select>
</mapper>

package com.andrew.mappers;
import java.util.List;
import com.andrew.model.Student;
public interface StudentMapper {
    public int add(Student student);
    public int update(Student student);
    public int delete(Integer id);
    public Student findById(Integer id);
    public List<Student> find();
    public Student findStudentWithAddress(Integer id);
}

<?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.andrew.mappers.StudentMapper">
    <resultMap type="Student" id="StudentResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
    </resultMap>
    <resultMap type="Student" id="StudentAddressResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        <association property="address" column="addressId" select="com.andrew.mappers.AddressMapper.findById"></association>
    </resultMap>
    <insert id="add" parameterType="Student">
        insert into t_student values(null, #{name}, #{age})
    </insert>
    <update id="update" parameterType="Student">
        update t_student set name=#{name},age=#{age} where id=#{id}
    </update>
    <delete id="delete" parameterType="Integer">
        delete from t_student where id=#{id}
    </delete>
    <select id="findById" parameterType="Integer" resultType="Student">
        select * from t_student where id=#{id}
    </select>
    <select id="find" resultMap="StudentAddressResult">
        select * from t_student
    </select>
    <select id="findStudentWithAddress" resultMap="StudentAddressResult" parameterType="Integer">
        select * from t_student t1,t_address t2 where t1.addressId=t2.id and t1.id=#{id}
    </select>
</mapper>

package com.andrew.service;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.andrew.mappers.StudentMapper;
import com.andrew.model.Student;
import com.andrew.util.SqlSessionFactoryUtil;
public class StudentAddressTest {
    private static Logger logger=Logger.getLogger(StudentTest.class);
    private SqlSession sqlSession=null;
    private StudentMapper studentMapper=null;
    @Before
    public void setUp() throws Exception {
        sqlSession = SqlSessionFactoryUtil.openSession();
        studentMapper = sqlSession.getMapper(StudentMapper.class);
    }
    @After
    public void tearDown() throws Exception {
        sqlSession.close();
    }
    @Test
    public void testFindStudentWithAddress() {
        logger.info("查询学生和地址");
        Student student = studentMapper.findStudentWithAddress(2);
        System.out.println(student);
    }
}
运行结果：
Student [id=2, name=李四, age=20, address=Address [id=2, sheng=河北省, shi=石家庄市, qu=新华区]]