MyBatis总结(二十五)--任务34：MyBatis_映射文件_select_resultMap_关联查询_collection定义关联集合封装规则

红太狼 2022-05-12 08:10 196阅读 0赞

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

![70][]

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

<resultMap type="com.atguigu.mybatis.bean.Department" id="MyDept">
    		<id column="did" property="id"/>
    		<result column="dept_name" property="departmentName"/>
    		
    		<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>

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 + "]";
    	}
    	
    	
    
    }

[70]: /images/20220512/d9dbc6faa1c44f81863f02f4cd842c9b.png