一、resultMap自定义结果集映射规则

示例如下：

接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Employee;

public interface EmployeeMapper {

    public Employee getEmpById(Integer id);

}

mapper定义：

<?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.mybatis.dao.EmployeeMapper">

    <!--

    自定义某个javaBean的封装规则

	type：自定义规则的Java类型

	id:唯一标示id，方便引用

	-->

    <resultMap id="EmpMap" type="com.mybatis.bean.Employee">

        <!--

        指定主键列的封装规则

		id定义主键会底层有优化；

		column：指定哪一列

		property：指定对应的javaBean属性

		-->

        <id column="id" property="id"/>

        <!-- 定义普通列封装规则 -->

        <result column="last_name" property="lastName"/>

        <!-- 其他不指定的列会自动封装：但是最好只要写resultMap就把全部的映射规则都写上。 -->

        <result column="email" property="email"/>

        <result column="gender" property="gender"/>

    </resultMap>

    <!--public Employee getEmpById(Integer id);-->

    <!-- resultMap:自定义结果集映射规则；  -->

    <select id="getEmpById" resultMap="EmpMap">

		select * from tbl_employee where id=#{id}

	</select>

</mapper>

测试代码：

package com.mybatis.demo;

import java.io.*;

import java.util.*;

import com.mybatis.bean.Employee;

import com.mybatis.dao.EmployeeMapper;

import org.apache.ibatis.io.*;

import org.apache.ibatis.session.*;

import org.junit.Test;

public class MyTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {

        String resource = "mybatis-config.xml";

        InputStream inputStream = Resources.getResourceAsStream(resource);

        return new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test

    public void testResultMap() throws IOException {

        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession openSession = sqlSessionFactory.openSession(true);

        try {

            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);

            Employee employee = mapper.getEmpById(1);

            System.out.println(employee);

        } finally {

            openSession.close();

        }

    }

}

二、resultMap使用场景

(一)、查询Employee的同时查询员工对应的部门。

1、联合查询：级联属性封装结果集。

员工实体类Employee

package com.mybatis.bean;

public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private Integer gender;

    private Department dept;

    public Employee() {

    }

    public Employee(String lastName, String email, Integer gender) {

        this.lastName = lastName;

        this.email = email;

        this.gender = gender;

    }

    public Employee(Integer id, String lastName, String email, Integer gender) {

        this.id = id;

        this.lastName = lastName;

        this.email = email;

        this.gender = gender;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getLastName() {

        return lastName;

    }

    public void setLastName(String lastName) {

        this.lastName = lastName;

    }

    public String getEmail() {

        return email;

    }

    public void setEmail(String email) {

        this.email = email;

    }

    public Integer getGender() {

        return gender;

    }

    public void setGender(Integer gender) {

        this.gender = gender;

    }

    public Department getDept() {

        return dept;

    }

    public void setDept(Department dept) {

        this.dept = dept;

    }

    @Override

    public String toString() {

        return "Employee{" +

                "id=" + id +

                ", lastName='" + lastName + '\'' +

                ", email='" + email + '\'' +

                ", gender=" + gender +

                ", dept=" + dept +

                '}';

    }

}

部门实体类Deptment

package com.mybatis.bean;

public class Department {

    private Integer id;

    private String departmentName;

    public Department() {

    }

    public Department(Integer id, String departmentName) {

        this.id = id;

        this.departmentName = departmentName;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getDepartmentName() {

        return departmentName;

    }

    public void setDepartmentName(String departmentName) {

        this.departmentName = departmentName;

    }

    @Override

    public String toString() {

        return "Department{" +

                "id=" + id +

                ", departmentName='" + departmentName + '\'' +

                '}';

    }

}

建立部门表及修改员工表的sql脚本如下：

CREATE TABLE tbl_dept(

	id INT(11) PRIMARY KEY AUTO_INCREMENT,

	dept_name VARCHAR(255)

);

alter table tbl_employee add column d_id int(11);

alter table tbl_employee add constraint fk_emp_dept

foreign key(d_id) references tbl_dept(id);

示例如下：

接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Employee;

public interface EmployeeMapper {

    public Employee getEmpByIdWithDept(Integer id);

}

mapper定义：

<?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.mybatis.dao.EmployeeMapper">

    <!--联合查询：级联属性封装结果集-->

    <resultMap id="EmpMap" type="com.mybatis.bean.Employee">

        <id column="id" property="id"/>

        <result column="last_name" property="lastName"/>

        <result column="gender" property="gender"/>

        <result column="did" property="dept.id"/>

        <result column="dept_name" property="dept.departmentName"/>

    </resultMap>

    <!--public Employee getEmpById(Integer id);-->

    <select id="getEmpByIdWithDept" resultMap="EmpMap">

        SELECT e.id id,e.last_name last_name,e.gender gender,e.d_id d_id,

		d.id did,d.dept_name dept_name FROM tbl_employee e,tbl_dept d

		WHERE e.d_id=d.id AND e.id=#{id}

    </select>

</mapper>

测试代码：

package com.mybatis.demo;

import java.io.*;

import java.util.*;

import com.mybatis.bean.Employee;

import com.mybatis.dao.EmployeeMapper;

import org.apache.ibatis.io.*;

import org.apache.ibatis.session.*;

import org.junit.Test;

public class MyTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {

        String resource = "mybatis-config.xml";

        InputStream inputStream = Resources.getResourceAsStream(resource);

        return new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test

    public void testResultMap() throws IOException {

        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession openSession = sqlSessionFactory.openSession(true);

        try {

            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);

            Employee employee = mapper.getEmpByIdWithDept(1);

            System.out.println(employee);

        } finally {

            openSession.close();

        }

    }

}

2、联合查询：使用association定义关联的单个对象的封装规则

示例如下：

接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Employee;

public interface EmployeeMapper {

    public Employee getEmpByIdWithDept(Integer id);

}

mapper定义：

<?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.mybatis.dao.EmployeeMapper">

    <!--使用association定义关联的单个对象的封装规则-->

    <resultMap id="EmpMap" type="com.mybatis.bean.Employee">

        <id column="id" property="id"/>

        <result column="last_name" property="lastName"/>

        <result column="gender" property="gender"/>

        <!--

        association可以指定联合的javaBean对象

		property="dept"：指定哪个属性是联合的对象

		javaType:指定这个属性对象的类型[不能省略]

		-->

        <association property="dept" javaType="com.mybatis.bean.Department">

            <id column="did" property="id"/>

            <result column="dept_name" property="departmentName"/>

        </association>

    </resultMap>

    <!--public Employee getEmpById(Integer id);-->

    <select id="getEmpByIdWithDept" resultMap="EmpMap">

        SELECT e.id id,e.last_name last_name,e.gender gender,e.d_id d_id,

		d.id did,d.dept_name dept_name FROM tbl_employee e,tbl_dept d

		WHERE e.d_id=d.id AND e.id=#{id}

    </select>

</mapper>

测试代码：

package com.mybatis.demo;

import java.io.*;

import java.util.*;

import com.mybatis.bean.Employee;

import com.mybatis.dao.EmployeeMapper;

import org.apache.ibatis.io.*;

import org.apache.ibatis.session.*;

import org.junit.Test;

public class MyTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {

        String resource = "mybatis-config.xml";

        InputStream inputStream = Resources.getResourceAsStream(resource);

        return new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test

    public void testResultMap() throws IOException {

        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession openSession = sqlSessionFactory.openSession(true);

        try {

            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);

            Employee employee = mapper.getEmpByIdWithDept(1);

            System.out.println(employee);

        } finally {

            openSession.close();

        }

    }

}

3、使用association进行分步查询

DeptmentMapper接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Department;

public interface DeptmentMapper {

    public Department getDeptById(Integer id);

}

DeptmentMapper.xml定义

<?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.mybatis.dao.DeptmentMapper">

    <!--public Department getDeptById(Integer id);-->

    <select id="getDeptById" resultType="com.mybatis.bean.Department">

        select id,dept_name departmentName from tbl_dept where id=#{id}

    </select>

</mapper>

EmployeeMapper接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Employee;

public interface EmployeeMapper {

    public Employee getEmpByIdWithDept(Integer id);

}

EmployeeMapper.xml定义：

<?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.mybatis.dao.EmployeeMapper">

    <!--

        使用association进行分步查询：

		1、先按照员工id查询员工信息

		2、根据查询员工信息中的d_id值去部门表查出部门信息

		3、部门设置到员工中；

	-->

    <resultMap type="com.mybatis.bean.Employee" id="MyEmpByStep">

        <id column="id" property="id"/>

        <result column="last_name" property="lastName"/>

        <result column="email" property="email"/>

        <result column="gender" property="gender"/>

        <!-- association定义关联对象的封装规则

            select:表明当前属性是调用select指定的方法查出的结果

            column:指定将哪一列的值传给这个方法

            流程：使用select指定的方法（传入column指定的这列参数的值）查出对象，并封装给property指定的属性

         -->

        <association property="dept"

                     select="com.mybatis.dao.DeptmentMapper.getDeptById"

                     column="d_id">

        </association>

    </resultMap>

    <select id="getEmpByIdWithDept" resultMap="MyEmpByStep">

       select * from tbl_employee where id=#{id}

    </select>

</mapper>

测试代码：

package com.mybatis.demo;

import java.io.*;

import java.util.*;

import com.mybatis.bean.Department;

import com.mybatis.bean.Employee;

import com.mybatis.dao.DeptmentMapper;

import com.mybatis.dao.EmployeeMapper;

import org.apache.ibatis.io.*;

import org.apache.ibatis.session.*;

import org.junit.Test;

public class MyTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {

        String resource = "mybatis-config.xml";

        InputStream inputStream = Resources.getResourceAsStream(resource);

        return new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test

    public void testResultMap() throws IOException {

        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession openSession = sqlSessionFactory.openSession(true);

        try {

            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);

            Employee employee = mapper.getEmpByIdWithDept(1);

            System.out.println(employee);

            System.out.println(employee.getDept());

        } finally {

            openSession.close();

        }

    }

}

4、延迟加载(懒加载、按需加载)

Employee==>Dept：
每次查询Employee对象的时候，部门信息在使用的时候再去查询；
只需在分步查询的基础之上加上两个配置：

<settings>

	<setting name="lazyLoadingEnabled" value="true"/>

	<setting name="aggressiveLazyLoading" value="false"/>

</settings>

(二)、查询部门的同时查询出该部门的所有员工。

1、嵌套结果集的方式，使用collection标签定义关联的集合类型的属性

Department实体类修改如下：

package com.mybatis.bean;

import java.util.List;

public class Department {

    private Integer id;

    private String departmentName;

    private List<Employee> emps;

    public Department() {

    }

    public Department(Integer id, String departmentName) {

        this.id = id;

        this.departmentName = departmentName;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getDepartmentName() {

        return departmentName;

    }

    public void setDepartmentName(String departmentName) {

        this.departmentName = departmentName;

    }

    public List<Employee> getEmps() {

        return emps;

    }

    public void setEmps(List<Employee> emps) {

        this.emps = emps;

    }

    @Override

    public String toString() {

        return "Department{" +

                "id=" + id +

                ", departmentName='" + departmentName + '\'' +

                ", emps=" + emps +

                '}';

    }

}

示例如下：

接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Department;

public interface DeptmentMapper {

    public Department getDeptByIdWithEmp(Integer id);

}

mapper定义：

<?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.mybatis.dao.DeptmentMapper">

    <!--嵌套结果集的方式，使用collection标签定义关联的集合类型的属性封装规则  -->

    <resultMap id="MyDept" type="com.mybatis.bean.Department">

        <id column="did" property="id"/>

        <result column="dept_name" property="departmentName"/>

        <!--

			collection定义关联集合类型的属性的封装规则

			ofType:指定集合里面元素的类型

		-->

        <collection property="emps" ofType="com.mybatis.bean.Employee">

            <id column="eid" property="id"/>

            <result column="last_name" property="lastName"/>

            <result column="email" property="email"/>

            <result column="gender" property="gender"/>

        </collection>

    </resultMap>

    <select id="getDeptByIdWithEmp" resultMap="MyDept">

        SELECT d.id did,d.dept_name dept_name,

				e.id eid,e.last_name last_name,e.email email,e.gender gender

		FROM tbl_dept d

		LEFT JOIN tbl_employee e

		ON d.id=e.d_id

		WHERE d.id=#{id}

    </select>

</mapper>

测试代码：

package com.mybatis.demo;

import java.io.*;

import java.util.*;

import com.mybatis.bean.Department;

import com.mybatis.bean.Employee;

import com.mybatis.dao.DeptmentMapper;

import com.mybatis.dao.EmployeeMapper;

import org.apache.ibatis.io.*;

import org.apache.ibatis.session.*;

import org.junit.Test;

public class MyTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {

        String resource = "mybatis-config.xml";

        InputStream inputStream = Resources.getResourceAsStream(resource);

        return new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test

    public void testResultMap() throws IOException {

        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession openSession = sqlSessionFactory.openSession(true);

        try {

            DeptmentMapper mapper=openSession.getMapper(DeptmentMapper.class);

            Department department=mapper.getDeptByIdWithEmp(1);

            System.out.println(department);

        } finally {

            openSession.close();

        }

    }

}

2、分步查询

示例代码：

EmployeeMapper接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Employee;

import java.util.List;

public interface EmployeeMapper {

    public List<Employee> getEmpsByDeptId(Integer deptId);

}

EmployeeMapper.xml文件定义：

<?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.mybatis.dao.EmployeeMapper">

    <select id="getEmpsByDeptId" resultType="com.mybatis.bean.Employee">

       select * from tbl_employee where d_id=#{deptId}

    </select>

</mapper>

DeptmentMapper接口定义：

package com.mybatis.dao;

import com.mybatis.bean.Department;

public interface DeptmentMapper {

    public Department getDeptByIdWithEmpStep(Integer id);

}

DeptmentMapper.xml文件定义：

<?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.mybatis.dao.DeptmentMapper">

    <resultMap id="MyDeptStep" type="com.mybatis.bean.Department">

        <id column="id" property="id"/>

        <id column="dept_name" property="departmentName"/>

        <collection property="emps"

                    select="com.mybatis.dao.EmployeeMapper.getEmpsByDeptId"

                    column="id"/>

    </resultMap>

    <select id="getDeptByIdWithEmpStep" resultMap="MyDeptStep">

      select id,dept_name departmentName from tbl_dept where id=#{id}

    </select>

</mapper>

测试代码：

package com.mybatis.demo;

import com.mybatis.bean.Department;

import com.mybatis.dao.DeptmentMapper;

import org.apache.ibatis.io.Resources;

import org.apache.ibatis.session.SqlSession;

import org.apache.ibatis.session.SqlSessionFactory;

import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import org.junit.Test;

import java.io.IOException;

import java.io.InputStream;

public class MyTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {

        String resource = "mybatis-config.xml";

        InputStream inputStream = Resources.getResourceAsStream(resource);

        return new SqlSessionFactoryBuilder().build(inputStream);

    }

    @Test

    public void testResultMap() throws IOException {

        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        SqlSession openSession = sqlSessionFactory.openSession(true);

        try {

            DeptmentMapper mapper = openSession.getMapper(DeptmentMapper.class);

            Department department = mapper.getDeptByIdWithEmpStep(2);

            System.out.println(department);

        } finally {

            openSession.close();

        }

    }

}

扩展：多列的值传递过去：

　　将多列的值封装map传递；
　　column="{key1=column1,key2=column2}"
　　fetchType="lazy"：表示使用延迟加载；
　　　　- lazy：延迟加载
　　　　- eager：立即加载

<?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.mybatis.dao.DeptmentMapper">

    <resultMap id="MyDeptStep" type="com.mybatis.bean.Department">

        <id column="id" property="id"/>

        <id column="dept_name" property="departmentName"/>

        <!-- 扩展：多列的值传递过去：

			将多列的值封装map传递；

			column="{key1=column1,key2=column2}"

		fetchType="lazy"：表示使用延迟加载；

				- lazy：延迟

				- eager：立即

	    -->

        <collection property="emps"

                    select="com.mybatis.dao.EmployeeMapper.getEmpsByDeptId"

                    column="{deptId=id}" fetchType="lazy"/>

    </resultMap>

    <select id="getDeptByIdWithEmpStep" resultMap="MyDeptStep">

      select id,dept_name departmentName from tbl_dept where id=#{id}

    </select>

</mapper>

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