mybatis-查询（resultMap,关联集合）-15

痛定思痛。 2022-03-17 08:38 187阅读 0赞

# mybatis**更多资料请访问 [www.itkc8.com][]** #

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<Employee> employees;\}  
  
接口

public Department getDepartmentByIdPlus(Integer id);  
1  
sql映射文件

<resultMap id="myDept" type="com.stayreal.mybatis.Department">  
            <id column="did" property="id"/>  
            <result column="dept\_name" property="name"/>  
              
            <collection property="employees" ofType="com.stayreal.mybatis.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="getDepartmentByIdPlus"  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>  
  
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'\}\[Employee\{id=1, //lastName='Jerry', email='Jerry@qq.com', gender='1'\}, //Employee\{id=3, lastName='Jerry', email='Jerry@qq.com', //gender='1'\}\]  
  
第二种方式：分步查询方式  
public Department getDepartmentByIdStep(Integer id);  
1  
  
        <resultMap id="myDeptStep" type="com.stayreal.mybatis.Department">  
            <id column="id" property="id"/>  
            <result column="dept\_name" property="name"/>  
            <collection property="employees" select="com.stayreal.mybatis.EmployeeMapperPlus.getEmpsByDeptId"  
                    column="id">  
            </collection>  
        </resultMap>  
        <select id="getDepartmentByIdStep"  resultMap="myDeptStep">  
                    select id,dept\_name name from tbl\_dept where id = \#\{id\}  
        </select>  
  
 Department dept = mapper.getDepartmentByIdStep(2);// 分步查询  collection  
//Department\{id=2, name='ceshi'\}  
//\[Employee\{id=1, lastName='null', email='Jerry@qq.com', gender='1'\}, Employee\{id=3, lastName='null', email='Jerry@qq.com', gender='1'\}\]

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[https://blog.csdn.net/apple\_5/article/details/72953946][https_blog.csdn.net_apple_5_article_details_72953946]

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[https_blog.csdn.net_apple_5_article_details_72953946]: https://blog.csdn.net/apple_5/article/details/72953946