Question

使用LINQ to SQL

db.Products.Where(c => c.ID == 1).Skip(1).Take(1).ToList();

执行

SELECT [t1].[ID], [t1].[CategoryID], [t1].[Name], [t1].[Price], [t1].[Descripti
n], [t1].[IsFeatured], [t1].[IsActive]
FROM (
    SELECT ROW_NUMBER() OVER (ORDER BY [t0].[ID], [t0].[CategoryID], [t0].[Name
, [t0].[Price], [t0].[Description], [t0].[IsFeatured], [t0].[IsActive]) AS [ROW
NUMBER], [t0].[ID], [t0].[CategoryID], [t0].[Name], [t0].[Price], [t0].[Descrip
ion], [t0].[IsFeatured], [t0].[IsActive]
    FROM [dbo].[Products] AS [t0]
    WHERE [t0].[ID] = @p0
    ) AS [t1]
WHERE [t1].[ROW_NUMBER] BETWEEN @p1 + 1 AND @p1 + @p2
ORDER BY [t1].[ROW_NUMBER]
-- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [1]
-- @p1: Input Int (Size = 0; Prec = 0; Scale = 0) [1]
-- @p2: Input Int (Size = 0; Prec = 0; Scale = 0) [1]

它使用ROW_NUMBER进行分页......很好。

现在，我正在尝试使用LINQ to SQL生成的关系来分页数据。使用查询...

var cat = db.Categories.Where(c => c.ID == 1).SingleOrDefault();
cat.Products.Where(c => c.ID == 1).Skip(1).Take(1).ToList();

SELECT [t0].[ID], [t0].[Name]
FROM [dbo].[Categories] AS [t0]
WHERE [t0].[ID] = @p0
-- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [1]
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.1

SELECT [t0].[ID], [t0].[CategoryID], [t0].[Name], [t0].[Price], [t0].[Descriptio
n], [t0].[IsFeatured], [t0].[IsActive]
FROM [dbo].[Products] AS [t0]
WHERE [t0].[CategoryID] = @p0
-- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [1]
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.1

现在ROW_NUMBER和分页的使用已经消失了......所有产品的CategoryID = 1 ......为什么它会获得所有行？

Answer 1

我认为这是因为该类别在记忆中。你隐含地要求它获得该类别的产品。这个隐含的数据请求用于填充，然后在内存中（此时类别在此处）执行查询。

我认为它相当于：

var cat = db.Categories.Where(c => c.ID == 1).SingleOrDefault();
var prods = db.Products.Where(c => c.ID == 1).ToList();
var r = prods.Where(p.CategoryID == cat.ID).Skip(1).Take(1);

注意意义，如果猫在内存中发生变化怎么办？收藏的大小可能会有所不同。

注意：感谢您的头痛：）

Answer 2

你试过了吗？

var cat = db.Categories.Where(c => c.ID == 1);
var prod = cat.Products.Where(c => c.ID == 1).Skip(1).Take(1).ToList();

Answer 3

您尚未分配第二个LINQ查询的输出。因此'cat'仍然是第一个查询。

查询LINQ to SQL关系

3 个答案: