流利的NHibernate-HasOne with Where子句 [英] Fluent NHibernate - HasOne With Where Clause

问题描述

使用Fluent NHibernate，我可以说出与我的User类的一对多关系:

with Fluent NHibernate i can map a one to many relationship against my User class by saying:

HasMany(x => x.Membership)
    .KeyColumn("UserID")
    .Where("Deleted = 0");

这按预期方式工作，因为它仅获取尚未删除的成员资格记录.不说我有一个名为最新会员资格"的字段，我知道这将为每个用户返回一条记录，我想说:

This works as expected that it only grabs the Membership records which have not been deleted. No say i have a field called Latest against the Membership where i know this would return one record per user, i'd like to be able to say:

HasOne(x => x.CurrentMembership)
    .Where("Current = 1");

但是没有Where方法.我知道我可以这样说:

But there is no Where method. I know i could do this in code by saying:

public virtual Membership CurrentMembership
    { get { return Membership.Single(m => m.Current); } }

但是，这不允许我对此属性执行LINQ查询.过去，我只是接受这作为限制，但是从性能方面来看，它确实开始对我产生影响.

But this doesn't allow me to do LINQ queries against this property. I'd just accepted this as a limitation in the past but it really is starting to bite me in terms of performance.

如果有人可以提供帮助，我将非常感谢.

I'd really appreciate it if someone could help.

推荐答案

HasOne(x => x.CurrentMembership)
    .Where("Current = 1");

如果一个实体与另一个实体具有"HasOne"关系，则它只能链接到一件事，因此Where方法是没有意义的.如果您的代码无意中没有将旧成员资格更新为Current = 0，那么它将有2个CurrentMembership实例可以链接到该实例，您会被搞砸了.

If an entity has a "HasOne" relationship to another, then there is only one thing it can link to so a Where method doesn't make sense. If your code accidentally doesn't update the old membership to have Current=0, then there will be 2 instances of CurrentMembership that it could link to and you'd be pretty screwed.

我认为您的数据库设计有问题.我想实现此效果的最佳方法是在User表上具有CurrentMembershipID，然后可以使用HasOne直接链接到该表.这将减少数据库的开销(您不必在成员资格表上存储当前"列)，它将有效地执行您要查找的操作.而且，它避免了用户拥有多个成员身份且当前设置为1的用户.

I think that you have a problem in your database design. The best way that I can think of implementing this is is to have a CurrentMembershipID on your User table and then you can link directly to it with a HasOne. This is less overhead for your database (you don't have to store a Current column on your membership table) and it will effectively do what you're looking for. Also, it avoids a user having more than one membership having current set to 1.

这篇关于流利的NHibernate-HasOne with Where子句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！