Linq-to-Entities / Linq-to-SQL，一种数据轮询方法更有效吗？

Question

Are the following two examples different and if so, which is more efficient?

var user = (from u in db.Users where u.Id == userId select u).Single();

and

var user = db.Users.Single(p => p.Id == userId);

Answer 1

They are functionally equivalent. There could be slight differences in how they are implemented in the various LINQ providers, but I would expect almost exactly equal performance. The LINQ to SQL provider for example produces the exact same SQL for both queries:

SELECT [t0].[Id], [t0].[Name]
FROM [dbo].[User] AS [t0]
WHERE [t0].[Id] = @p0

I expect that the same applies to the Entity Framework.

If I had to pick one I'd choose the second version because it is more concise with no loss of clarity. In fact I would say it is more clear - there is less keyword noise so the business logic stands out more.

Answer 2

它们最终将是完全相同的（SQL和效率明智）。

Answer 3

They are the same. The compiler should produce the same outcome for both LINQ syntax.