resultMap_关联查询_collection 使用规则

1、项目结构

2、Department.java

package com.atguigu.mybatis.bean;

import java.util.List;

public class Department {
    
    private Integer id;
    private String departmentName;
    private List<Employee> emps;
    
    public List<Employee> getEmps() {
        return emps;
    }
    public void setEmps(List<Employee> emps) {
        this.emps = emps;
    }
    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 + ", emps=" + emps + "]";
    }
    
    
}

3、Employee.java

package com.atguigu.mybatis.bean;

public class Employee {

    private Integer id;
    private String lastName;
    private String email;
    private String gender;
    private Department dept;
    
    public Department getDept() {
        return dept;
    }
    public void setDept(Department dept) {
        this.dept = dept;
    }
    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;
    }
    @Override
    public String toString() {
        return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + "]";
    }
    public Employee(Integer id, String lastName, String email, String gender) {
        super();
        this.id = id;
        this.lastName = lastName;
        this.email = email;
        this.gender = gender;
    }
    public Employee() {
        super();
        // TODO Auto-generated constructor stub
    }
    
    
}

4、DepartmentMapper.java

package com.atguigu.mybatis.dao;

import com.atguigu.mybatis.bean.Department;

public interface DepartmentMapper {
    
    public Department getDeptById(Integer id);
    
    public Department getDeptByIdPlus(Integer id);

}

5、EmployeeMapperPlus.java

package com.atguigu.mybatis.dao;

import com.atguigu.mybatis.bean.Employee;

public interface EmployeeMapperPlus {
    
    
    public Employee getEmpById(Integer id);
    
    public Employee getEmpAndDept(Integer id) ;
    
    public Employee getEmpByIdStep(Integer id) ;
}

6、MybatisTest.java

package com.atguigu.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.atguigu.mybatis.bean.Department;
import com.atguigu.mybatis.bean.Employee;
import com.atguigu.mybatis.dao.DepartmentMapper;
import com.atguigu.mybatis.dao.EmployeeMapperPlus;

public class MybatisTest {
    
    private SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }
  
    @Test
    public void test3() throws IOException {
        SqlSessionFactory sqlSessionFactory =getSqlSessionFactory();
        //1、获取到的SqlSession不会自动提交
        SqlSession openSession= sqlSessionFactory.openSession();
        try {
            
            DepartmentMapper mapper=openSession.getMapper(DepartmentMapper.class);
            Department department=mapper.getDeptByIdPlus(1);
            
            System.out.println(department);
            System.out.println(department.getEmps());
            //3、手动提交
            openSession.commit();
            
        } finally {
            openSession.close();
        }
    }
    
}

7、DepartmentMapper.xml

<?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.atguigu.mybatis.dao.DepartmentMapper">
    
    <!-- public Department getDeptById(Integer id); -->
    <select id="getDeptById" resultType="com.atguigu.mybatis.bean.Department">
        select id,dept_name departmentName from tbl_dept where id=#{id}
    </select>
    
    <!-- 
        private Integer id;
        private String departmentName;
        private List<Employee> emps;
            public Department getDeptByIdPlus(Integer id); -->
    <resultMap type="com.atguigu.mybatis.bean.Department" id="Mydept">
        <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 
                指定集合里元素类型
        -->
        <collection property="emps" ofType="com.atguigu.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="getDeptByIdPlus" 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>

注：collection定义关联集合类型的属性的封装规则 

　　　　ofType:指定集合里元素类型，其他与association一样

　　　　<collection property="emps" ofType="com.atguigu.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>

8、EmployeeMapperPlus.xml（此项目中没用到）

<?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.atguigu.mybatis.dao.EmployeeMapperPlus">
    
    <resultMap type="com.atguigu.mybatis.bean.Employee" id="MySimpleEmp">
        <id column="id" property="id"/>
        <result column="last_name" property="lastName"/>
    </resultMap>
    <!-- public Employee getEmpById(Integer id); -->
    <select id="getEmpById" resultMap="MySimpleEmp">
        select * from tbl_employee where id=#{id}
    </select>
 
 
    
    <!-- 场景一： 
            查询employee的同时查询员工对应的部门
            SELECT e.id id,e.last_name lastName,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=2
    -->
    <!-- 
        联合查询：级联属性封装结构集
     -->
    <resultMap type="com.atguigu.mybatis.bean.Employee" id="MyDifEmp">
        <id column="id" property="id"/>
        <result column="email" property="email"/>
        <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>
    <resultMap type="com.atguigu.mybatis.bean.Employee" id="MyDifEmp2">
        <id column="id" property="id"/>
        <result column="email" property="email"/>
        <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：指定这个属性的类型
         -->
        <association property="dept" javaType="com.atguigu.mybatis.bean.Department">
            <id column="did" property="id"/>
            <result column="dept_name" property="departmentName"/>
        </association>
    </resultMap>
    <!-- public Employee getEmpAndDept(Integer id) ; -->
    <select id="getEmpAndDept" resultMap="MyDifEmp2"> 
        SELECT e.id id,e.email email,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>
    
    
    
    <!-- 使用association分步查询：
            1、先按照员工id查询员工信息
            2、根据查询员工信息的d_id值去部门部门表查出部门信息
            3、部门设置到员工中
     -->
    <resultMap type="com.atguigu.mybatis.bean.Employee" id="MyEmpStep">
        <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:指定将那一列的值的传给这个方法
            流程：使用select指定的方法（传入column指定的这列参数值）查出对象，并封装给property指定的属性
            -->
        <association property="dept" 
                select="com.atguigu.mybatis.dao.DepartmentMapper.getDeptById"
                        column="d_id">            
        </association>
    </resultMap>
    <!-- public Employee getEmpByIdStep(Integer id) ; -->
    <select id="getEmpByIdStep" resultMap="MyEmpStep">
        select * from tbl_employee where id=#{id}
    </select>
    
    <!-- =================================association=================================================== -->
    <!-- 
        场景二：
            DepartmentMapper.xml中
     -->
    
    
</mapper>

9、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>

<!-- 
    <settings>
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>
     -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <!-- 配置数据库连接信息 -->
            <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="111111" />
            </dataSource>
        </environment>
    </environments>
    
       <mappers>
           
        <mapper resource="com/atguigu/mybatis/dao/EmployeeMapperPlus.xml"/>
        <mapper resource="com/atguigu/mybatis/dao/DepartmentMapper.xml"/>
       </mappers> 
   
</configuration>