mybatis-210720-01---映射文件_select_resultMap_collection定义关联集合封装

mybatis-210720-01—映射文件_select_resultMap_collection定义关联集合封装.md

• DepartmentMapper.java
• DepartmentMapper.xml(笔记在这儿)
• EmployeeMapper.java
• EmployeeMapper.xml
• MybatisTest.java
• Department.java
• Employee.java

---

<!--
		场景2
			查询部门的时候，把对应所有的员工信息查询出来
-->

DepartmentMapper.java

package com.bgy.mybatis.dao;
import com.bgy.mybatis.bean.Department;

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

---

DepartmentMapper.xml(笔记在这儿)

<?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.bgy.mybatis.dao.DepartmentMapper">
	
	<!-- 嵌套结果集的方式，使用collection标签定义关联集合类型的属性封装规则 -->
	<!--
		要查询的是这些内容
		did dept_name || eid last_name email gender
		从 || 开始划分	左边是tbl_dept信息   右边是tbl_employee信息  
	-->
	<resultMap type="com.bgy.mybatis.bean.Department" id="MyDept">
		<id column="did" property="id"/>
		<result column="dept_name" property="departmentName"/>
		
		<!--
			assocation是用来定义对象的
			collection是用来定义关联集合的属性的封装规则
			
			ofType：
				指定集合里面元素的类型
		-->
		<collection property="emps" 
			ofType="com.bgy.mybatis.bean.Employee">
			
			<!-- 定义这个集合元素的封装规则 -->
			<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>

---

EmployeeMapper.java

package com.bgy.mybatis.dao;

import java.util.List;
import com.bgy.mybatis.bean.Employee;

public interface EmployeeMapper {
	
	public List<Employee> getEmpsByDeptId(Integer deptId);
}

---

EmployeeMapper.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.bgy.mybatis.dao.EmployeeMapper">
	
	<!--
		场景2
			查询部门的时候，把对应所有的员工信息查询出来
	-->
	<select id="getEmpsByDeptId" resultType="com.bgy.mybatis.bean.Employee">
		select 
			* 
		from
			tbl_employee
		where 	
			d_id=#{deptId} 
	</select>
</mapper>

---

MybatisTest.java

package com.bgy.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.jupiter.api.Test;

import com.bgy.mybatis.bean.Department;
import com.bgy.mybatis.dao.DepartmentMapper;

class MybatisTest {
	
	public SqlSessionFactory getSqlSessionFactory() throws IOException {
		String resource = "mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		return new SqlSessionFactoryBuilder().build(inputStream);
	}

	
	/**
	 * 测试collection定义关联集合封装规则
	 * @throws IOException
	 */
	@Test
	public void test04() throws IOException{
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession sqlSession = sqlSessionFactory.openSession();
		
		try {
			DepartmentMapper mapper = sqlSession.getMapper(DepartmentMapper.class);
			Department department = mapper.getDeptByIdPlus(1);
			
			System.out.println(department.getDepartmentName());
			System.out.println(department.getEmps());
		} finally {
			sqlSession.close();
		}
	}
}

---

Department.java

package com.bgy.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 + "]";
	}
}

Employee.java

package com.bgy.mybatis.bean;
import org.apache.ibatis.type.Alias;

/*
 	批量起别名的情况下，使用@Alias注解为某个类型执指定新的别名，叫emp
 	如果bean包下有子包，子包也叫Employee，那就要使用注解起别名了
 */
@Alias("emp")
public class Employee {
	
	private Integer id;
	private String lastName;
	private String email;
	private String gender;
	private Department dept;
	
	public Employee() {
		super();
	}
	
	public Employee(Integer id, String lastName, String email, String gender) {
		super();
		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 Department getDept() {
		return dept;
	}

	public void setDept(Department dept) {
		this.dept = dept;
	}

	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 + ", dept="
				+ dept + "]";
	}
}