Mybatis联合查询（一）

Mybatis的简单联合查询操作：

实体类：

Employee:

package com.test.mybatis;

public class Employee {
    private Integer id;
    private String lastName;
    private String email;
    private String gender;
    private Depart depart;
    
    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 String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public Depart getDepart() {
        return depart;
    }
    public void setDepart(Depart depart) {
        this.depart = depart;
    }
    @Override
    public String toString() {
        return "Employee [id=" + id + ", lastName=" + lastName + ", email="
                + email + ", gender=" + gender + ", depart=" + depart + "]";
    }
    
    
    
}

Depart:

package com.test.mybatis;

public class Depart {
    private int id;
    private String departName;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getDepartName() {
        return departName;
    }
    public void setDepartName(String departName) {
        this.departName = departName;
    }
    @Override
    public String toString() {
        return "Depart [id=" + id + ", departName=" + departName + "]";
    }
    
    
}

mybatis-config.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
    PUBLIC     "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                    <property name="username" value="root"/>
                    <property name="password" value="root"/>
                </dataSource>
            </environment>
        </environments>
        <!-- 将我们写好的sql映射文件（EmployeeMapper.xml）一定要注册到 mybatis-config.xml中-->
        <mappers>
            <mapper resource="EmployeeMapper.xml"/>
        </mappers>
    </configuration>

EmployeeMapper接口：

package com.test.mybatis.dao;

import com.test.mybatis.Employee;

public interface EmployeeMapper {
    
    
    public Employee getEmpAndDept(Integer id);
}

EmployeeMapper.xml:

对接口进行实现;

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mtbatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.test.mybatis.dao.EmployeeMapper">
    <!-- 
　　　　　方法一：
        联合查询：级联属性封装结果集
     -->
    <resultMap type="com.test.mybatis.Employee" id="MyEmp">
        <!-- 
            指定主键列的封装规则
            id定义主键会底层优化
            column：指定哪一列
            property：指定对应的JavaBean
         -->
        <id column="id" property="id"/>
        <!-- 普通列封装 -->
        <result column="last_name" property="lastName"/>
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
        <result column="did" property="depart.id"/>
        <result column="dept_name" property="depart.departName"/>
    </resultMap>
    <!-- 
　　　　方法二：
        使用association定义单个对象的封装规则
     -->
    <resultMap type="com.test.mybatis.Employee" id="MyEmp2">
        <id column="id" property="id"/>
        <result column="last_name" property="lastName"/>
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
        <!-- 
        association可以指定联合的Javabean对象
        property:指定那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="depart" javaType="com.test.mybatis.Depart">
            <id column="did" property="id"/>
            <id column="dept_name" property="departName"/>
        </association>
    </resultMap>
     <!-- 
         查询Employee的同时查询员工对应的部门
      -->
      <select id="getEmpAndDept" resultMap="MyEmp2">
            SELECT e.id id,e.last_name last_name,e.email email,e.gender gender,d.id did,d.dept_name dept_name 
            from 
            tbl_depat d,tbl_employee  e 
            where d.id=e.d_id AND e.id=#{id}               
      </select>
    </mapper>

测试类：

package com.test.mybatis.test;

import java.io.IOException;
import java.io.InputStream;

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 com.test.mybatis.Employee;
import com.test.mybatis.dao.EmployeeMapper;

public class MyBatisTest {
    //读取配置文件，得到SQLSessionFactory
    public SqlSessionFactory getSqlSessionFactory() throws IOException{
        String resource="mybatis-config.xml";
        InputStream is=Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(is);
    }
    @Test
    public void test01() throws IOException{
        //获取sqlSessionFactory对象
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        //获取sqlSession
        //代表和数据库的一次对话，用完必须关闭，相当于connection，都是非线程安全。每次使用都应该获取新的对象
        SqlSession openSession = sqlSessionFactory.openSession();
        try{
        //获取接口的实现类对象
        //会为接口自动的创建一个代理对象，代理对象去执行增删查改方法
        //mapper接口没有实现类，但是mybatis会为这个接口生成一个代理对象
        //（将接口和xml进行绑定）
        EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
        Employee emp = mapper.getEmpAndDept(6);
        System.out.println(emp+":"+emp.getDepart());
        
        }finally{
            openSession.close();
        }
    }

}