Mybatis多对多处理

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1. 数据库中建立 3张表，2个对象，一张关联表

2. 关联表对应java 对象

 private int id;    private DataTag dataTag;    private StorageData storageData;

3. DataTag

  private int tagId;    private String tagName;    private int parent;    private String userId;    private List<StorageData> storageDataList;

4. StorageData

    private String dataId;    private String description;    private byte[] content;    private String fileName;    private String ext;

根据需求决定对象是否加另一对象的List,通过tag要找dataList，所以tag中含 storageDataList

5.xml

<resultMap type="DataTag" id="dataTagMap">        <id property="tagId" column="tagId" />        <result property="tagName" column="tagName" />        <result property="parent" column="parent" />        <result property="userId" column="userId" />  </resultMap>  <resultMap type="DataTag" id="dataTagStorageDataMap" extends="dataTagMap">      <collection property="storageDataList" ofType="StorageData">          <id property="dataId" column="dataId" />          <result property="description" column="description" />          <result property="ext" column="ext" />          <result property="fileName" column="fileName" />          <result property="content" column="content" />      </collection>  </resultMap>

 <select id="findTagByUserId" parameterType="string" resultMap="dataTagStorageDataMap">    SELECT        t.tagId,        t.tagName,        t.parent,        t.userId,        d.dataId,        d.description,        d.ext,        d.fileName,        d.content    FROM t_tag t    LEFT JOIN t_tag_storage_data td    ON t.tagId = td.tagId    LEFT JOIN t_storage_data d    ON td.dataId = d.dataId    WHERE userId = #{userId}  </select>

6. 插入操作，维护关系表

在stoargeData 中加

 public void saveRelativity(TagStorageDataLink tagDataLink);

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