为什么下面的 linq to sql 查询会生成子查询?

问题描述

我做了以下查询:

var list = from book in books
          where book.price > 50
          select book;

list = list.Take(50);

我希望上面能产生类似的东西:

I would expect the above to generate something like:

SELECT top 50 id, title, price, author
FROM Books
WHERE price > 50

但它会产生:

SELECT
[Limit1].[C1] as [C1]
[Limit1].[id] as [Id], 
[Limit1].[title] as [title], 
[Limit1].[price] as [price], 
[Limit1].[author]
FROM (SELECT TOP (50) 
             [Extent1].[id] as as [Id], 
             [Extent1].[title] as [title], 
             [Extent1].[price] as [price], 
             [Extent1].[author] as [author]
      FROM Books as [Extent1]
      WHERE [Extent1].[price] > 50
     ) AS [Limit1]

为什么上面的linq查询会生成子查询，C1从哪里来?

Why does the above linq query generate a subquery and where does the C1 come from?

推荐答案

你仍然可以像这样让它更干净:

You could still make it cleaner like this:

var c = (from co in db.countries
                    where co.regionID == 5
                    select co).Take(50);

这将导致:

Table(country).Where(co => (co.regionID = Convert(5))).Take(50)

相当于:

SELECT TOP (50) [t0].[countryID], [t0].[regionID], [t0].[countryName], [t0].[code]
FROM [dbo].[countries] AS [t0]
WHERE [t0].[regionID] = 5

评论，不一定是因为使用单独的 Take()，您仍然可以像这样使用它:

Comments, Its Not necessarily because with separate Take(), you can still use it like this:

var c = (from co in db.countries
                     where co.regionID == 5
                     select co);
            var l = c.Take(50).ToList();

结果和之前一样.

SELECT TOP (50) [t0].[countryID], [t0].[regionID], [t0].[countryName], [t0].[code]
FROM [dbo].[countries] AS [t0]
WHERE [t0].[regionID] = @p0

您编写 IQueryable = IQueryable.Take(50) 的事实是这里的棘手部分.

The fact that you wrote IQueryable = IQueryable.Take(50) is the tricky part here.