Question

我的音乐相关数据库中有三个实体：视频，相册和流派。视频和专辑都可以有多种类型，因此我尝试将它们与多对多关联链接起来。我在DB中有什么：

Videos:
   Id (int)
   ... (many other columns)

Albums:
   Id (int)
   ... (many other columns)

Genre:
   Id (int)
   Name (string)

Item_Genres: (table we are mapping many-to-many with)
   Id (int)
   objectType (here I have "album" for albums and "video" for videos)
   objectId (id from either Albums or Videos table)
   genreId (Id of the appropriate genre)

我可以使用多对多来将类型映射到视频和专辑，但我需要获取所有类型特别视频。我怎么能这样做？

目前我在视频映射中有这个：

    <set name="Genres" table="item_genres" lazy="true">
        <key>
            <column name="objectId" not-null="true"/>
        </key>
        <many-to-many class="Repositories.Entities.Genre">
            <column name="genreId" not-null="true"/>
        </many-to-many>
    </set>

当要求 video.Genres 时，我有该视频的类型和具有相同ID的相册。

Answer 1

您可以尝试像这样定义视频映射：

<set name="Genres" table="item_genres" lazy="true" where="objectType = 'video'">
    <key>
        <column name="objectId" not-null="true"/>
    </key>
    <many-to-many class="Repositories.Entities.Genre">
        <column name="genreId" not-null="true"/>
    </many-to-many>
</set>

where =“objectType ='video'应确保您只获取视频而非专辑。

nHibernate具有元值的多对多

1 个答案: