nhibernate - 当我删除父引用时，如何让 NHibernate 删除子引用？

Question

我有一个 NewsFeed 对象映射如下:

<class name="NewsFeed">
    <id name="NewsFeedId">
        <generator class="guid"/>
    </id>

    <property name="FeedName" not-null="true" />
    <property name="FeedURL" not-null="true" />
    <property name="FeedIsPublished" not-null="true" />
</class>

可以拥有一组他们可能感兴趣的选定提要的用户，映射如下:

<class name="SystemUser">
    <id name="SystemUserId">
        <generator class="guid"/>
    </id>


    <set name="SelectedNewsFeeds" table="SystemUserSelectedNewsFeeds" cascade="all">
        <key column="SystemUserId" />
        <many-to-many column="NewsFeedId" class="NewsFeeds.NewsFeed, Domain"/>
    </set>

</class>

我想要发生的是当我删除父 NewsFeed 时，所有 SelectedNewsFeed 引用也被删除，而不必加载每个 SystemUser 并手动删除 NewsFeed。

实现这一目标的最佳方法是什么？

更新 :在删除 NewsFeed 时，使用cascade="all-delete-orphan"而不是"all"仍然会导致异常:

The DELETE statement conflicted with the REFERENCE constraint "FKC8B9DF81601F04F4". The conflict occurred in database "System", table "dbo.SystemUserSelectedNewsFeeds", column 'NewsFeedId'.

Answer 1

JMCD

你的第二种方法:

Another alternative is to break the many-to-many relationship with a join class in the middle which nHiberate would be able to determine parent-child relationships and the cascade should work.

实际上是 nHibernate 人员在他们的文档中推荐的。

Don't use exotic association mappings.

Good usecases for a real many-to-many associations are rare. Most of the time you need additional information stored in the "link table". In this case, it is much better to use two one-to-many associations to an intermediate link class. In fact, we think that most associations are one-to-many and many-to-one, you should be careful when using any other association style and ask yourself if it is really neccessary.

使用两个一对多关联增加了将其他属性轻松添加到“订阅”的灵活性，例如该特定订阅的通知首选项。