MyBatis关联查询（对象嵌套对象）

    Mybatis 查询对象中嵌套其他对象的解决方法有两种，一种是用关联另一个resultMap的形式，如

<association property="office"  javaType="Office" resultMap="officeMap"/>

     

<mapper namespace="com.dixn.oa.modules.sys.dao.RoleDao">
    
   <resultMap type="Office" id="officeMap">
    	<id property="id" column="id" />
    	<result property="name" column="office.name" />
    	<result property="code" column="office.code" />
    </resultMap>
    
    <resultMap id="roleResult" type="Role">
		<id property="id" column="id" />
		<result property="name" column="name" />
		<result property="enname" column="enname" />
		<result property="roleType" column="roleType" />
		<result property="dataScope" column="dataScope" />
		<result property="remarks" column="remarks" />
		<result property="useable" column="useable" />
		<association property="office"  javaType="Office" resultMap="officeMap"/>
		<collection property="menuList" ofType="Menu">
			<id property="id" column="menuList.id" />
		</collection>
		<collection property="officeList" ofType="Office">
			<id property="id" column="officeList.id" />
		</collection>
	</resultMap>
	
    <sql id="roleColumns">
    	a.id,
    	a.office_id AS "office.id",
    	a.name,
    	a.enname,
    	a.role_type AS roleType,
	a.data_scope AS dataScope,
	a.remarks,
	a.create_by AS "createBy.id",
	a.create_date,
	a.update_by AS "updateBy.id",
	a.update_date,
	a.del_flag,
    	o.name AS "office.name",
    	o.code AS "office.code",
    	a.useable AS useable,
    	a.is_sys AS sysData
    </sql>
    
<select id="get" resultMap="roleResult">
	SELECT
	<include refid="roleColumns"/>
	rm.menu_id AS "menuList.id",
	ro.office_id AS "officeList.id"
	FROM sys_role a
	JOIN sys_office o ON o.id = a.office_id
	LEFT JOIN sys_role_menu rm ON rm.role_id = a.id
	LEFT JOIN sys_role_office ro ON ro.role_id = a.id
	WHERE a.id = #{id}
</select>

    

     另一种联合查询 (一对一)的实现，但是这种方式有“N+1”的问题，不建议使用

 

 

 <resultMap id="roleResult" type="Role">
		<id property="id" column="id" />
		<result property="name" column="name" />
		<result property="enname" column="enname" />
		<result property="roleType" column="roleType" />
		<result property="dataScope" column="dataScope" />
		<result property="remarks" column="remarks" />
		<result property="useable" column="useable" />
		<association property="office"  javaType="Office"     column="id" select="getOfficeById"/>
		<collection property="menuList" ofType="Menu">
			<id property="id" column="menuList.id" />
		</collection>
		<collection property="officeList" ofType="Office">
			<id property="id" column="officeList.id" />
		</collection>
	</resultMap>

 

 
    
    <select id="getOfficeById"  resultType="Office">
        select o.name AS "office.name",o.code AS "office.code" from sys_office o where o.id = #{id}
    </select> 

    以上就是两种对象内嵌套对象查询的实现。