問題描述

為什么我會收到此錯誤:

Why I am getting this error:

LINQ to Entities 不支持方法Single".考慮使用First"方法.

           public ActionResult Details(int id)
Line 27:   {              
             var result = (from d in _db.MovieSet
Line 29:     where d.Id == id
Line 30:     select d).Single();
            //
            //
           } 

代碼編譯安全，但只有在調(diào)用相應(yīng)部分時才會中斷.我是 LINQ 的新手，因此不知道哪些方法適用于 LINQtoSQL 或 LINQtoEntities.這意味著更多的錯誤！我們無法以這種方式記住所有方法.

Code compiles safe, but only breaks if call is made to the respective section. I am new to LINQ, therefore do not know which methods are for LINQtoSQL or LINQtoEntities. This means more errors! We cannot remember all methods this way.

我的問題是，如果適用于某些類型/場景的方法有限制，為什么它們會出現(xiàn)在 Intellisense 中?

My question is, if there are limitations to the methods applicable to certain types / scenarios, why do they appear in Intellisense?

任何有助于了解是否支持的解決方法/技術(shù)?

Any work-around / technique helpful to have an idea if one is supported ?

推薦答案

Microsoft 有一個完整的 Linq to Entities 中支持和不支持的方法列表.去那里可以找到這些信息.

Microsoft has a complete list of supported and unsupported methods in Linq to Entities. That's where to go to find out this information.

您會注意到 Single 和 SingleOrDefault 方法實際上在分頁方法部分被列為不支持".

You'll notice that the Single and SingleOrDefault methods are in fact listed as "not supported" in the section on Paging Methods.

正如 Jared 所指出的，編譯器在編譯時不知道您使用的是哪個提供程序，因此它無法強(qiáng)制執(zhí)行提供程序可能實現(xiàn)或可能不實現(xiàn)的擴(kuò)展方法的編譯時安全性.您將不得不依賴文檔.

As Jared pointed out, the compiler does not know at compile time which provider you are using, so it has no way to enforce compile-time safety of extension methods that the provider may or may not implement. You'll have to rely on the documentation instead.

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