mybatis-查询（resultMap,关联集合）-15

来源：互联网发布：苏州软件学院编辑：程序博客网时间：2024/06/05 03:19

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);

sql映射文件

    <!--         private Integer id;        private String name;        private List<Employee> employees;        -->        <!-- 嵌套结果集的方式-->        <!--public Department getDepartmentByIdPlus(Integer id);-->        <resultMap id="myDept" type="com.stayreal.mybatis.Department">            <id column="did" property="id"/>            <result column="dept_name" property="name"/>            <!-- collection定义关联集合类型的属性封装规则            offType:指定集合中的元素类型            -->            <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);

<!--public Department getDepartmentByIdStep(Integer id);-->        <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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