实体框架4，继承vs扩展？-EntityFramework4,inheritingvsextending?

5  

I have tried similar thing as you describe, and the main problem I see, is that u can't create ObjectSet for derived type. So you will not have ObjectSet repository. If you derive all your Entities from for example BusinessObject entity, you will be able to work only with ObjectSet. If you want to query only Person repository, you can write query like Context.BusinessObjectSet.OfType().ToList() but i think it will not generate proper SQL under the hood and will first get full BusinessObject rows and then filter out Person entities in memory. So I guess it will have huge performance impact.

我尝试过类似于你描述的东西，我看到的主要问题是你不能为派生类型创建ObjectSet 。所以你不会有ObjectSet 存储库。如果从例如BusinessObject实体派生所有实体，则只能使用ObjectSet 。如果你只想查询Person存储库，你可以编写类似Context.BusinessObjectSet.OfType （）。ToList（）的查询，但我认为它不会生成正确的SQL，并将首先获得完整的BusinessObject行然后过滤out内存中的Person实体。所以我猜它会产生巨大的性能影响。

9  

I'm a little late to the party, but I've been having the same questions as you regarding inheritance in EF and found a pretty good summary for you to read. It's an excerpt from Julie Lerman's book Programming Entity Framework.

我参加派对的时间有点晚了，但是我在EF的遗传方面遇到了同样的问题，并为你找了一个很好的总结。这是朱莉·勒曼（Julie Lerman）的“编程实体框架”（Programming Entity Framework）一书的摘录。

After reading it, here's my conclusions on the topic:

阅读之后，这是我对这个主题的结论：

1) In general, what are the pros/cons of inheritance vs extending - The pros really depend on the table strategy you choose. See How to choose an Inheritance Strategy - MSDN Blog. However, they are only "pros" on the assumption that you have already decided to use inheritance at all. And that is not a decision to take lightly.

1）一般来说，继承与扩展的优缺点是什么 - 优点实际上取决于您选择的表策略。请参见如何选择继承策略 - MSDN博客。但是，假设您已经决定使用继承，它们只是“专业人士”。这不是一个轻率的决定。

The cons are many, but the biggest is the inability to add an existing entity into the database as a derived entity. For example: I have a Student which inherits from Person. There is a Person record for John Smith. Some time later I need John Smith to be a Student. Well too bad. That's not possible. (At least not without circumventing EF with a stored procedure).

缺点很多，但最大的是无法将现有实体作为派生实体添加到数据库中。例如：我有一个继承自Person的学生。 John Smith有一个Person记录。一段时间后，我需要约翰史密斯成为一名学生。太糟糕了。那是不可能的。 （至少在没有通过存储过程规避EF的情况下）。

2) In my specific example above, what would be more appropriate? - In your example you should just add those columns (entityId, datecreated, datemodified) to tables that need them. You could use a Complex Type for datecreated and datemodified, but that wouldn't be necessary unless you're a very strict DRY guy. Even then, it might be overkill. The reason is that once you have an entity, you can never add that entity to another derived table. A Person (which is a BaseEntity) can not be added as a Student later. Also, writing LINQ queries would be far more complex than needed. Alex already showed that.

2）在我上面的具体例子中，哪个更合适？ - 在您的示例中，您应该将这些列（entityId，datecreated，datemodified）添加到需要它们的表中。您可以使用复杂类型进行datecreated和datemodified，但除非您是一个非常严格的DRY家伙，否则这不是必需的。即便如此，它可能有点矫枉过正。原因是，一旦有了实体，就永远不能将该实体添加到另一个派生表中。一个人（这是一个BaseEntity）以后不能作为学生添加。另外，编写LINQ查询会比需要复杂得多。 Alex已经证明了这一点。

3) If my example is crappy for either or both, what is a good example for using inheritance and for using extending? - Generally, if you can make your base-type abstract, inheritance might work for you. But you should still consider other options first. If your base type will be directly instantiated somewhere, just use composition. Inheritance gets very troublesome when it comes to actually querying and inserting records.

3）如果我的例子对于其中一个或两个都很糟糕，那么使用继承和使用扩展的好例子是什么？ - 通常，如果您可以创建基类型抽象，继承可能适合您。但你应该首先考虑其他选择。如果您的基本类型将直接在某处实例化，只需使用合成。在实际查询和插入记录时，继承变得非常麻烦。

In summary, just because you can do inheritance in EF does not mean you should. If you can get away with an inheritance-free design, then by all means do it.

总之，仅仅因为你可以在EF中进行继承并不意味着你应该这样做。如果你能摆脱无继承设计，那么一定要做到。

3  

One disadvantage of using inheritance in your model is that you won't be able to surface your model through WCF Data Services (OData) as it doesn't currently support derived entities.

在模型中使用继承的一个缺点是，您将无法通过WCF数据服务（OData）显示模型，因为它当前不支持派生实体。