Mybatis3.1-[tp-30-31]-select_resultMap_关联查询_级联属性封装结果__association定义关联对象封装规则

笔记要点

出错分析与总结

在全局配置中,映射dao包下的全部:

<mapper>
    <package name="com.dao"/>
    </mappers>

工程组织

1.定义接口

package com.dao;
import com.bean.*;
public interface EmployeeMapperPlus {

    public Employee getEmpAndDept(Integer id);//关联查询
    public Employee getEmpAndDept2(Integer id); //关联查询 ,使用association
    public Employee getEmpById(Integer id);

}

2.定义XML映射文件

<?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.dao.EmployeeMapperPlus">
   <!--ResultMap ;自定义结果集映射规则;
        type: 自定义规则的Java类型;id: 唯一的标识,方便引用-->
    <resultMap id="MySimpleEmp" type="com.bean.Employee">
        <!--指定主键列的封装规则,id定义主键,底层会有优化规则;
        column : 指定结果集的具体的那一列; property:指定的JavaBean对应的属性-->
        <id column="id" property="id"/>
        <!--定义普通列的封装规则-->
        <result column="last_name" property="lastName"/>
        <!--,其他不指定的列会自动封装;但是, 我们只要写ResultMap,就把剩下的映射全部都写上-->
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
    </resultMap>

    <!--public Employee getEmpById(Integer id);   注意进行更改为resultMap-->
    <select id="getEmpById" resultMap="MySimpleEmp">
        select * from tbl_employee where id=#{id}
    </select>

    <!--场景1   ,方法1:使用级联属性的方式
        查询Employee的同时查询员工对应的部门Employee.dept=Department.id;
        输出员工对应的部门的全部信息:
                 id  last_name  gender     did  dept_name
    -->
    <resultMap id="MyDifEmp" type="com.bean.Employee">
        <!--column : 指定结果集的具体的那一列; property:指定的JavaBean对应的属性-->
        <id column="id" property="id"/>
        <result column="last_name" property="lastName"/>
        <result column="gender" property="gender"/>
        <result column="email" property="email"/>
        <result column="did" property="dept.id"/>
        <result column="dept_name" property="dept.departmentName"/>
    </resultMap>
    <!--public Employee getEmpAndDept2(Integer id);   //association 定义封装规则!-->

    <select id="getEmpAndDept" resultMap="MyDifEmp">
          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,email
            FROM tbl_employee e,tbl_dept d
            WHERE e.`d_id`=d.`id` AND e.id=#{id};
    </select>

    <!--方法2:-使用association可以指定联合的javaBean的对象
     -->
    <resultMap id="MyDifEmp2" type="com.bean.Employee">
        <!--column : 指定结果集的具体的那一列; property:指定的JavaBean对应的属性-->
        <id column="id" property="id"/>
        <result column="last_name" property="lastName"/>
        <result column="gender" property="gender"/>
        <result column="email" property="email"/>

    <!--使用association可以指定联合的javaBean的对象;(定义单个对象的封装规则!)
        property="dept";指定那个属性是联合的对象;javaType="dept";指定那个属性对象的类型;-->
        <association property="dept" javaType="com.bean.Department">
            <id column="did" property="id"/>
            <result column="dept_name" property="departmentName"/>
        </association>

    </resultMap>
    <!--public Employee getEmpAndDept2(Integer id);   //关联查询-->

    <select id="getEmpAndDept2" resultMap="MyDifEmp2">
          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,email
            FROM tbl_employee e,tbl_dept d
            WHERE e.`d_id`=d.`id` AND e.id=#{id};
    </select>

</mapper>

3.编写测试代码

package com.test.resultMap;

import com.bean.Employee;
import com.dao.EmployeeMapperPlus;
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 test_tp30 {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream=Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }
    @Test
    public void test06() throws Exception{

        SqlSession openSession = getSqlSessionFactory().openSession();
        try {
            EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
            System.out.println("--------多表关联查询,级联属性的封装结果!--------");
            Employee employee = mapper.getEmpAndDept(1);
            System.out.println(employee);
            System.out.println("--------多表关联查询,使用association进行连接!--------");
            Employee employee2 = mapper.getEmpAndDept2(1);
            System.out.println(employee2);
            openSession.commit();//默认是不自动提交数据的,需要我们自己手动提交
        }finally {
            openSession.close();
        }
    }
}

测试结果

--------多表关联查询,级联属性的封装结果!--------
DEBUG 12-01 10:37:03,938 ==>  Preparing: 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,email FROM tbl_employee e,tbl_dept d WHERE e.`d_id`=d.`id` AND e.id=?;   (BaseJdbcLogger.java:145)
DEBUG 12-01 10:37:03,958 ==> Parameters: 1(Integer)  (BaseJdbcLogger.java:145)
DEBUG 12-01 10:37:03,968 <==      Total: 1  (BaseJdbcLogger.java:145)
Employee{id=1, lastName='jerry', email='jerry@163.com', gender='1'}
--------多表关联查询,使用association进行连接!--------
DEBUG 12-01 10:37:03,969 ==>  Preparing: 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,email FROM tbl_employee e,tbl_dept d WHERE e.`d_id`=d.`id` AND e.id=?;   (BaseJdbcLogger.java:145)
DEBUG 12-01 10:37:03,969 ==> Parameters: 1(Integer)  (BaseJdbcLogger.java:145)
DEBUG 12-01 10:37:03,970 <==      Total: 1  (BaseJdbcLogger.java:145)
Employee{id=1, lastName='jerry', email='jerry@163.com', gender='1'}

Process finished with exit code 0