为什么下面的LINQ to SQL的查询生成一个子查询？ [英] Why did the following linq to sql query generate a subquery?

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);

我希望上面的产生是这样的：

I would expect the above to generate something like:

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

但它产生：

but it generates:

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查询生成一个子查询和哪里的C1来的？

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

推荐答案

您仍然可以使它更清洁是这样的：

You could still make it cleaner like this:

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

这会导致：

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

等同于：

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

编辑：评论，其因有独立承担（）不一定，你仍然可以使用这样的：

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();

，其结果将是和以前一样。

And the Result would be the same as before.

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

这是你写的事实的IQueryable = IQueryable.Take（50）是这里的棘手的部分。

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

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