Mybatis05_自定义映射ResultMap

Mybatis05_自定义映射ResultMap

1. 一对一，字段名和属性名不一致

   • 将查询结果的字段名设置别名对应上属性名

     <select id="getEmpById" resultType="Emp">
         select emp_id empId,emp_name empName,age,gender from emp where emp_id = #{emp_id}
     </select>
     

   • 在mybatis核心配置文件中的setting设置

     但是要保证字段名符合mysql的规则使用下划线，属性名符合java规则使用驼峰

     <settings>
             <setting name="mapUnderscoreToCamelCase" value="true"/>
     </settings>
         
     select * from emp where emp_id = #{emp_id}
     

   • 使用自定义映射

     resulType改为设置resultMap的id

     • id对应字段主键，result对应普通字段
     • column对应字段名，property对应属性名

     <resultMap id="EmpResultMap" type="Emp">
             <id column="emp_id" property="empId"></id>
             <result column="emp_name" property="empName"></result>
             <result column="age" property="age"></result>
             <result column="gender" property="gender"></result>
         </resultMap>
         
     <!--    Emp getEmpById(@Param("emp_id") int emp_id);-->
         <select id="getEmpById" resultMap="EmpResultMap">
             select * from emp where emp_id = #{emp_id}
         </select>
     

2. 一对多关系映射

   • 使用级联方式

     <select id="getEmpAndDeptById" resultMap="empAndDeptResultMap">
             select * from emp
             left join dept
             on emp.dept_id = dept.dept_id
             where emp_id = #{empId}
         </select>
     
     <resultMap id="empAndDeptResultMap" type="Emp">
         <id column="emp_id" property="empId"></id>
         <result column="emp_name" property="empName"></result>
         <result column="age" property="age"></result>
         <result column="gender" property="gender"></result>
         <result column="dept_id" property="dept.deptId"></result>
         <result column="dept_name" property="dept.deptName"></result>
     </resultMap>
     

   • 使用association

     <select id="getEmpAndDeptById" resultMap="empAndDeptResultMapAsso">
             select * from emp
             left join dept
             on emp.dept_id = dept.dept_id
             where emp_id = #{empId}
         </select>
     
     <resultMap id="empAndDeptResultMapAsso" type="Emp">
             <id column="emp_id" property="empId"></id>
             <result column="emp_name" property="empName"></result>
             <result column="age" property="age"></result>
             <result column="gender" property="gender"></result>
     <!--        association:处理多对一映射,即实体类属性
                 property:处理的实体类属性，javaType:属性的类型
                 column字段名property实体类属性的成员属性名-->
             <association property="dept" javaType="Dept">
                 <id column="dept_id" property="deptId"></id>
                 <result column="dept_name" property="deptName"></result>
             </association>
         </resultMap>
     

   • 使用分步查询

     <select id="getEmpandDeptByStepOne" resultMap="empAndDeptByStepResultMap">
             select * from emp where emp_id = #{empId}
         </select>
     
     <resultMap id="empAndDeptByStepResultMap" type="Emp">
             <id column="emp_id" property="empId"></id>
             <result column="emp_name" property="empName"></result>
             <result column="age" property="age"></result>
             <result column="gender" property="gender"></result>
     <!--    property映射的实体类属性
             select下一步查询的sql唯一标识
             column下一步查询的sql的查询条件-->
             <association property="dept"
                          select="com.canyan7n.mybatis.mapper.DeptMapper.getEmpAndDeptByStepTwo"
                          column="dept_id">
             </association>
         </resultMap>
         
         <select id="getEmpAndDeptByStepTwo" resultType="Dept">
             select * from dept where dept_id = #{deptId}
         </select>
     

3. 延迟加载

   • 延迟加载，默认值为false

     <setting name="lazyLoadingEnabled" value="true"/>
     

   • 按需加载，默认值为false

     <setting name="aggressiveLazyLoading" value="true"/>
     

4. 一对多映射

   • collection

     <!--    Dept getDeptAndEmpByDeptId(@Param("deptId") Integer deptId);-->
         <select id="getDeptAndEmpByDeptId" resultMap="DeptAndEmpResultMap">
             select * from dept left join emp on dept.dept_id = emp.dept_id where dept.dept_id = #{deptId}
         </select>
         
     <!--    collection-->
         <resultMap id="DeptAndEmpResultMap" type="Dept">
             <id column="dept_id" property="deptId"></id>
             <result column="dept_name" property="deptName"></result>
             <collection property="emps" ofType="Emp">
                 <id column="emp_id" property="empId"></id>
                 <result column="emp_name" property="empName"></result>
                 <result column="age" property="age"></result>
                 <result column="genger" property="gender"></result>
             </collection>
         </resultMap>
     

   • 分步

     <!--    Dept getDeptAndEmpByStepOne(@Param("deptId") Integer deptId);-->
     <select id="getDeptAndEmpByStepOne" resultMap="DeptAndEmpByStepResultMap">
         select * from dept where dept_id = #{deptId}
     </select>
     
     <!--    分步-->
     <resultMap id="DeptAndEmpByStepResultMap" type="Dept">
         <id column="dept_id" property="deptId"></id>
         <result column="dept_name" property="deptName"></result>
         <association property="emps"
                      select="com.canyan7n.mybatis.mapper.EmpMapper.getDeptAndEmpByStepTwo"
                      column="dept_id" fetchType="eager">
         </association>
     </resultMap>