ResultMap 使用collection实现多层嵌套

实体结构

现有三个实体需要层层嵌套，即一个A包含多个B，一个B包含多个C。
在这个例子里就是一个问卷包含多个问题，一个问题又包含多个选项。一对多关系

• 实体Questionnaire

public class Questionnaire extends BaseEntity {
    /** 问卷id */
    private Long id;
    
    /** 问卷标题 */
    private String title;
    
    /** 问卷状态 */
    private String status;
    
	/** 问卷关联问题 */
    private List<Question> questionList;
    
 }

• 实体Question 关联Questionnaire的id

public class Question extends BaseEntity {

    /** 问题id */
    private Long id;
    
    /** 关联问卷id */
    @Excel(name = "关联问卷id" )
    private Long questionnaireId;
    
    /** 问题内容 */
    @Excel(name = "问题内容" )
    private String questionContent;
    
    /** 问卷问题关联选项list */
    private List<QuestionItem> questionItemList;
 }

• 实体QuestionItem 关联Question 的id

public class QuestionItem extends BaseEntity {

    /**  题目id */
    private Long id;

    /** 问题id */
    private Long questionId;

    /** 选项内容 */
    private String itemContext;
 }

xml中实现

<resultMap type="Questionnaire" id="QuestionnaireResult">
        <result property="id" column="id"/>
        <result property="title" column="title"/>
        <result property="description" column="description"/>
        <result property="startTime" column="start_time"/>
        <result property="endTime" column="end_time"/>
        <result property="status" column="status"/>
        <result property="createBy" column="create_by"/>
        <result property="createTime" column="create_time"/>
        <result property="updateBy" column="update_by"/>
        <result property="updateTime" column="update_time"/>
        <result property="delFlag" column="del_flag"/>
        <result property="remark" column="remark"/>
        <collection property="questionList" javaType="ArrayList" ofType="Question" column="id" select="selectQuestionByQuestionnaireId"/>
    </resultMap>

    <resultMap id="QuestionResult" type="Question">
        <result property="id" column="id"/>
        <result property="questionnaireId" column="questionnaire_id"/>
        <result property="questionContent" column="question_content"/>
        <result property="problemType" column="problem_type"/>
        <result property="createBy" column="create_by"/>
        <result property="createTime" column="create_time"/>
        <result property="updateBy" column="update_by"/>
        <result property="updateTime" column="update_time"/>
        <result property="delFlag" column="del_flag"/>
        <result property="remark" column="remark"/>
        <collection property="questionItemList" javaType="ArrayList" ofType="QuestionItem" column="id" select="selectQuestionItemByQuestionId"/>
    </resultMap>

    <resultMap id="QuestionItemResult" type="QuestionItem">
        <result property="id" column="id"/>
        <result property="questionId" column="question_id"/>
        <result property="itemContext" column="item_context"/>
        <result property="createBy" column="create_by"/>
        <result property="createTime" column="create_time"/>
        <result property="updateBy" column="update_by"/>
        <result property="updateTime" column="update_time"/>
        <result property="delFlag" column="del_flag"/>
        <result property="remark" column="remark"/>
    </resultMap>

<select id="selectQuestionnaireById" parameterType="Long" resultMap="QuestionnaireResult">
        <include refid="selectQuestionnaireVo"/>
        where id = #{id}
        and del_flag = #{delFlag}
    </select>

    <select id="selectQuestionByQuestionnaireId" resultMap="QuestionResult">
        select * from buss_question where questionnaire_id = #{id}
    </select>

    <select id="selectQuestionItemByQuestionId" resultMap="QuestionItemResult">
        select * from buss_question_item where question_id = #{id}
    </select>

其中collection 中

• property 对应实体中的属性
• javaType 属性的类型，可以写成List，或者不写这个属性
• ofType 映射到集合中的实体类名
• column 传参参数
• select 关联查询语句

感谢 https://blog.youkuaiyun.com/chen_nianqing/article/details/106235069