实体框架4：为什么我不能得到派生实体的ObjectSet而不是ObjectQuery？ [英] Entity Framework 4: Why can't I get an ObjectSet of derived entities rather than an ObjectQuery?

问题描述

使用 _container.BaseEntities.OfType<投资>（） 我得到一个总是查询数据库的ObjectQuery。

因此，我宁愿拥有一个 ObjectSet< Investment> code>。

我不明白为什么EF不支持派生实体...还是这样做？ ;）

如果我将继续在EF（这将是愚蠢的）创建一个根实体，它与我所有的派生实体有关联，我将获得EntityCollections通过该一个根实体的导航属性为这些实体。但是必须有另一种方式...

干杯

解决方案

这就是它在EF ObjectContext API中的工作原理。如果您尝试为派生实体创建 ObjectSet ，您将获得：

ArgumentException：没有为指定的
实体类型投资定义的
EntitySets。如果
'Investment'是派生类型，则使用
代替基类型。参数名称：
TEntity

此外，一旦定义了继承，派生实体就没有导航属性。提供导航属性的关联更改为继承。

我还遵循您的，我不得不说我尝试了很多，但我永远不会得到你的行为。即使我直接调用Count到 ObjectSet ，我总是得到SQL查询（检查分析器）和数据库中的实体的数量 - 不在集合中。

I have an "Investment" entity that is derived from "BaseEntity".

With _container.BaseEntities.OfType<Investment>() I get an ObjectQuery that always queries the database.

Therefore I would rather have an ObjectSet<Investment>.

I can't understand why EF doesn't support this for derived entities... Or does it? ;)

If I would go ahead and create a "root entity" in EF (which would be silly) that has associations to all my derived entities, I would get EntityCollections for those entities through the navigation properties of that one root-entity. But there must be another way...

Cheers

解决方案

That is how it works in EF ObjectContext API. If you try to create ObjectSet for derived entity you will get:

ArgumentException: There are no EntitySets defined for the specified entity type 'Investment'. If 'Investment' is a derived type, use the base type instead. Parameter name: TEntity

Also once you define inheritance there are no navigation properties to derived entities. The association which offers navigation property is changed to inheritance.

I also followed your former questions which is probably source of this one and I have to say I tried a lot but I can never get your behavior. Even if I call Count directly to ObjectSet I always get SQL query (checked in the profiler) and count of entities in the database - not in the set.

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