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Mybatis学习笔记8 - resultMap自定义结果集映射规则
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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>
