许多到许多额外的列的NHibernate [英] many-to-many with extra columns nhibernate

问题描述

所以，我有两个表用户和组。这些表（在数据库中）喜欢用 UGlink 链接表。现在除了主 - 外键链接表有一个额外的列：日期

So I have two tables Users and Groups. These tables are (in the database) liked with a UGlink link table. Now except for the primary-foreign keys the link table have an extra column: Date.

据我所知，这意味着我必须有两个多到一，以中间的链接。

From what I understand this means that I have to have two Many-to-One, with the link "in the middle".

不过，因为我几乎从来不感兴趣的额外的列值，反正是有避免的联系？这就是我希望能够写：

However since I'm almost never is interested of the extra column value, is there anyway to avoid the link? That is I want to be able to write:

thisUser.Groups

以获得代替的基团，

to get the groups, instead of:

thisUser.UGlinks.Group

推荐答案

的多到许多，无配对表作为一个实体的显式映射 - 是在NHibernate的当然支载。因此，在情况下，在日期的列自动生成，或可为空的（不必通过应用程序/ NHiberante插入）的，我们能做到喜欢这里：<一HREF =htt​​p://nhforge.org/doc/nh/en/index.html相对=nofollow> 6.8。双向关联

The many-to-many, without the explicit mapping of the pairing table as an entity - is in NHibernate of course suported. So, in case, that the Date column is autogenerated, or nullable (does not have to be inserted by app/NHiberante), we can do it like here: 6.8. Bidirectional Associations

<class name="User">
    <id name="Id" column="Uid"/>
    ...
    <bag name="Groups" table="UGlink" lazy="true">
        <key column="Uid"/>
        <many-to-many class="Group" column="Gid"/>
    </bag>
</class>

<class name="Group">
    <id name="id" column="Gid"/>
    ...

    <!-- inverse end -->
    <bag name="Users" table="UGlink" inverse="true" lazy="true">
        <key column="Gid"/>
        <many-to-many class="User" column="Uid"/>
    </bag>
</class>

那么，我们有什么是一个映射，其中NHiberante不关心配对表，我们可以这样做：

So, what we have is a mapping, in which NHiberante does care about the pairing table, and we can do:

thisUser.Groups

但是，如果我可以建议，不要用去多到许多。该多到一与配对对象（我说）更好的解决方案，因为它会支持组，反之亦然搜索用户。

But if I could suggest, do not go with many-to-many. The many-to-one with pairing object is (I'd say) better solution, because it will support searching Users by Groups and vice versa.

请参阅第24章最佳实践，举：

不要使用复杂的关联映射。

良好的用例是罕见的。大多数时候，你需要存储在链接表的更多信息。在这种情况下，它是最好使用两个一一对多关联到一个中间链路类。事实上，我们认为大多数协会是一个一对多和多对一的，你应该使用其他任何关联的风格的时候要小心，问问自己，是否真的neccessary。

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.

下面是一些更详细的解释如何做到这一点没有太多的一对多： NHibernate的：如何重新present多对一对多带一个一对多的关系的关系？

Here is some more detailed explanation how to do it without many-to-many: Nhibernate: How to represent Many-To-Many relationships with One-to-Many relationships?

这篇关于许多到许多额外的列的NHibernate的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！