myBatis使用collection

collection 使用情景：数据库多表连接查询

--------------------------------entity------------------------------------------------

public class ExamDto {        private Long id;       private Timestamp startTime;       private List<ExamQuestion> listExamQuestion;       private ExamPaper examPaper;      private Integer version;

      ----------getter and setter--------

}

public class ExamQuestion {   private Integer examPaperId;    private Integer type;     private Double score;     private String title;

 ----------getter and setter---------
}  

------------------------Mapper---------------------------------

<resultMap id="resultItem" type="com.xxx.xxx.xxx.xxx.ExamDto">    <id column="id" property="id"/>    <result column="start_time" property="startTime"/>    <result column="end_time" property="endTime"/>    <collection property="listExamQuestion" resultMap="resultExamQuestion"/></resultMap><resultMap id="resultExamQuestion" type="com.xxxx.xxx.xxx.xxx.ExamQuestion">        <result column="q_exam_paper_id" property="examPaperId"/>        <result column="q_type" property="type"/>        <result column="q_score" property="score"/>        <result column="q_title" property="title"/></resultMap>

----------------------执行SQL-------------------------------------------

select  e.id,  e.start_time,  e.end_time,  p.id as p_id,  p.exam_id as p_exam_id,  q.exam_paper_id as q_exam_paper_id,  q.type as q_type,  q.score as q_score,  q.title as q_titlefrom t_exam eLEFT JOIN t_exxm_papxr p on p.exam_id = e.idLEFT JOIN t_exxm_quexxion q ON q.exam_paper_id = p.id
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