25、Mybatis进阶：MyBatis_映射文件_select_resultMap_关联查询_collection定义关联集合封装规则-程序员快看-教程，程序员编程资料站

本文内容来自上硅谷

主要介绍了collection的基本用法

本项目的目录结构如下

Junit

	@Test
	public void test06() throws IOException{
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		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());
		}finally{
			openSession.close();
		}
	}

DepartmentMapper

package com.atguigu.mybatis.dao;

import com.atguigu.mybatis.bean.Department;

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

	public Department getDeptByIdStep(Integer id);
}

xml

	<!--
	public class Department {
			private Integer id;
			private String departmentName;
			private List<Employee> emps;
	  did  dept_name  ||  eid  last_name  email   gender
	 -->

	<!--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 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
			ofType:指定集合里面元素的类型
		-->
		<collection property="emps" ofType="com.atguigu.mybatis.bean.Employee">
			<!-- 定义这个集合中元素的封装规则 -->
			<id column="eid" property="id"/>
			<result column="last_name" property="lastName"/>
			<result column="email" property="email"/>
			<result column="gender" property="gender"/>
		</collection>
	</resultMap>
	<!-- public Department getDeptByIdPlus(Integer id); -->
	<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>

javabean

此javabean中有个list集合，所以xml需要用collection这个标签来实现与javabean中list集合的映射

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
				+ "]";
	}
}

Employee

package com.atguigu.mybatis.bean;

import org.apache.ibatis.type.Alias;

@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 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 + "]";
	}
	
	

}