使用RresultMap中collection做嵌套查询-蒲公英云

使用RresultMap中collection做嵌套查询

怼烎@ 2024-04-01 09:33 137阅读 0赞

1.使用格式如下：

<collection column="传递给嵌套查询语句的字段参数"
            property="pojo对象中的集合属性" 
            ofType="集合属性中的pojo对象"
            select="嵌套的查询语句" > 
 </collection>

注意：<collection>标签中的column：是要传递给select查询语句的参数，如果传递多个参数，格式为column= “ {参数名1=表字段1,参数名2=表字段2}“ ；

2.实例

（2）实体类

@Data
public class SubjectVO implements Serializable {
    private static final long serialVersionUID = 1L;
    private String id;
    private String title;
    private Integer sort;
    private List<SubjectVO> children = new ArrayList<>();
}

（2）mapper.xml

<mapper namespace="com.atguigu.guli.service.edu.mapper.SubjectMapper">
    <resultMap id="nestedSubject" type="com.atguigu.guli.service.edu.entity.vo.SubjectVO">
        <id property="id" column="id"/>
        <result property="title" column="title"/>
        <result property="sort" column="sort"/>
        <collection column="id"
                    property="children"   
                    ofType="com.atguigu.guli.service.edu.entity.vo.SubjectVO"     
                    select="selectNestedListByParentId"/>
    </resultMap>
    <select id="selectNestedListByParentId" resultMap="nestedSubject">
        select id, sort, title
        from edu_subject
        where parent_id = #{parentId}
    </select>
</mapper>