FluentNHibernate:性能下降时,映射参考与NotFound.Ignore() [英] FluentNHibernate: Performance Penalty when mapping Reference with NotFound.Ignore()
问题描述
我用FluentNhibernate,我看到NHibernate的执行许多查询时,协会的引用与 NotFound.Ignore()
映射。
由于我的遗留数据库的引用完整性是有点蹩脚,我想知道,如果有一个变通方法,或者如果有一个替代的映射我可以使用。
例如:
//没有加载实体
参考及LT时查询;使用者名称>(X => X。 ,用户,用户ID)LazyLoad()可空()。
//当我打开我的实体
参考及LT执行了一百查询;使用者名称>(X => x.User,用户ID)。LazyLoad()可空()NOTFOUND 。忽视();
这是一个已知的问题不幸的是,有一个问题在NHibernate的JIRA( https://nhibernate.jira.com/browse/NH-1001 )
有一种变通方法,虽然,但它是不漂亮。在实体你需要做沿着这个路线的东西:
实体类{
私人诠释? _用户名;
私人用户的用户;
公众用户用户
{
获得{
如果(_userId == NULL)
返回NULL;
回报用户;
};
集合{
如果(价值== NULL)
_userId = NULL;
,否则
_userId = value.UserId;
_user =价值;
};
}
}
和在映射你将映射参考正常但没有未找到= ignore设置,但你也映射外键字段:
引用<使用者>(Reveal.Membmer< ;使用者>(_用户),用户ID)LazyLoad();
地图(Reveal.Membmer<&诠释GT;(_用户id))。可空()Not.Update()Not.Insert()。 //禁止更新和插入,使它们不与用户的映射有冲突。
基本上,你让NHibernate的运作正常的在_user字段,然后用_userId现场手工做的空检查。这样就避免了N + 1查询问题。不足之处是它的实体复杂,并会查询更难写。如果你希望能够使用用户属性在LINQ查询,例如,你将不得不暴露出内部_user场并使用它来代替。
I use FluentNhibernate and I see NHibernate performing many queries when references of associations are mapped with NotFound.Ignore()
.
Since the referential integrity of my legacy database is kinda crappy, I'd like to know if there's a workaround or if there's an alternative mapping I can use.
Example:
//no query when loading the entity
References<User>(x => x.User, "UserId").LazyLoad().Nullable();
//performs a hundred queries when I load my entities
References<User>(x => x.User, "UserId").LazyLoad().Nullable().NotFound.Ignore();
This is a known problem unfortunately, there is an issue in NHibernate JIRA (https://nhibernate.jira.com/browse/NH-1001)
There is a workaround though but it isn't pretty. In the Entity you need to do something along the lines of this:
class Entity {
private int? _userId;
private User user;
public User User
{
get {
if (_userId == null)
return null;
return user;
};
set {
if (value == null)
_userId = null;
else
_userId = value.UserId;
_user = value;
};
}
}
And in the mapping you would map the reference as normal but without the not-found = ignore setting but you also map the foreign key field:
References<User>(Reveal.Membmer<User>("_user"), "UserId").LazyLoad();
Map(Reveal.Membmer<int?>("_userId")).Nullable().Not.Update().Not.Insert(); // Suppress updates and inserts so that they don't conflict with the mapping of User.
Basically you let NHibernate operate as normal on the _user field and then use the _userId field to manually do the null check. This way you avoid the N+1 selects problem. The downside is that it complicates the Entity and will make queries harder to write. If you want to be able to use the User-property in a LINQ query for example you will have to expose the internal _user field and use that instead.
这篇关于FluentNHibernate:性能下降时,映射参考与NotFound.Ignore()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!