mybatis-查询（resultMap,关联集合）-15

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场景：查询部门下的所有员工

第一种方式：嵌套结果集方式 
第二种方式：分步查询方式

第一种方式：嵌套结果集方式
javaBean

public class Department {
    private Integer id;
    private String name;
    private List employees;}

接口

public Department getDepartmentByIdPlus(Integer id);
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sql映射文件

   
       
       
       
           
           
           
           
               
               
               
               
           
       
       
            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}
       

junit

 DepartmentMapper mapper = session.getMapper(DepartmentMapper.class);
                Department dept = mapper.getDepartmentByIdPlus(2);// 分步查询
                System.out.println(dept.toString());
                System.out.println(dept.getEmployees());
// Department{id=2, name='ceshi'}[Employee{id=1, //lastName='Jerry', email='[email protected]', gender='1'}, //Employee{id=3, lastName='Jerry', email='[email protected]', //gender='1'}]

第二种方式：分步查询方式
public Department getDepartmentByIdStep(Integer id);
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                                column="id">
           
       
       
                    select id,dept_name name from tbl_dept where id = #{id}
       

 Department dept = mapper.getDepartmentByIdStep(2);// 分步查询  collection
//Department{id=2, name='ceshi'}
//[Employee{id=1, lastName='null', email='[email protected]', gender='1'}, Employee{id=3, lastName='null', email='[email protected]', gender='1'}]
 

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https://blog.csdn.net/apple_5/article/details/72953946