c# - Entity Framework 4 中的 Linq 查询。糟糕的性能

Question

在我的项目中，我使用 EntityFramework 4 来处理数据。我通过一个简单的查询发现了可怕的性能问题。当我查看由 EF4 生成的 sql 查询的探查器时，我感到震惊。

我的实体数据模型中有一些表:

看起来很简单。我正在尝试从具有所有相关导航属性的指定类别中选择所有产品项目。

我写了这个 LINQ 查询:

ObjectSet<ProductItem> objectSet = ...; 
int categoryId = ...; 

var res = from pi in objectSet.Include("Product").Include("Inventory").Include("Inventory.Storage") 
where pi.Product.CategoryId == categoryId 
select pi;

EF 生成了这个 sql 查询:

SELECT   [Project1].[pintId1]          AS [pintId], 
[Project1].[pintId]           AS [pintId1], 
[Project1].[intProductId]     AS [intProductId], 
[Project1].[nvcSupplier]      AS [nvcSupplier], 
[Project1].[ nvcArticle]      AS [ nvcArticle], 
[Project1].[nvcBarcode]       AS [nvcBarcode], 
[Project1].[bIsActive]        AS [bIsActive], 
[Project1].[dtDeleted]        AS [dtDeleted], 
[Project1].[pintId2]          AS [pintId2], 
[Project1].[nvcName]          AS [nvcName], 
[Project1].[intCategoryId]    AS [intCategoryId], 
[Project1].[ncProductType]    AS [ncProductType], 
[Project1].[C1]               AS [C1], 
[Project1].[pintId3]          AS [pintId3], 
[Project1].[intProductItemId] AS [intProductItemId], 
[Project1].[intStorageId]     AS [intStorageId], 
[Project1].[dAmount]          AS [dAmount], 
[Project1].[mPrice]           AS [mPrice], 
[Project1].[dtModified]       AS [dtModified], 
[Project1].[pintId4]          AS [pintId4], 
[Project1].[nvcName1]         AS [nvcName1], 
[Project1].[bIsDefault]       AS [bIsDefault] 
FROM     (SELECT [Extent1].[pintId]         AS [pintId], 
[Extent1].[intProductId]   AS [intProductId], 
[Extent1].[nvcSupplier]    AS [nvcSupplier], 
[Extent1].[ nvcArticle]    AS [ nvcArticle], 
[Extent1].[nvcBarcode]     AS [nvcBarcode], 
[Extent1].[bIsActive]      AS [bIsActive], 
[Extent1].[dtDeleted]      AS [dtDeleted], 
[Extent2].[pintId]         AS [pintId1], 
[Extent3].[pintId]         AS [pintId2], 
[Extent3].[nvcName]        AS [nvcName], 
[Extent3].[intCategoryId]  AS [intCategoryId], 
[Extent3].[ncProductType]  AS [ncProductType], 
[Join3].[pintId1]          AS [pintId3], 
[Join3].[intProductItemId] AS [intProductItemId], 
[Join3].[intStorageId]     AS [intStorageId], 
[Join3].[dAmount]          AS [dAmount], 
[Join3].[mPrice]           AS [mPrice], 
[Join3].[dtModified]       AS [dtModified], 
[Join3].[pintId2]          AS [pintId4], 
[Join3].[nvcName]          AS [nvcName1], 
[Join3].[bIsDefault]       AS [bIsDefault], 
CASE 
WHEN ([Join3].[pintId1] IS NULL) THEN CAST(NULL AS int) 
ELSE 1 
END AS [C1] 
FROM   [ProductItem] AS [Extent1] 
INNER JOIN [Product] AS [Extent2] 
ON [Extent1].[intProductId] = [Extent2].[pintId] 
LEFT OUTER JOIN [Product] AS [Extent3] 
ON [Extent1].[intProductId] = [Extent3].[pintId] 
LEFT OUTER JOIN (SELECT [Extent4].[pintId]           AS [pintId1], 
[Extent4].[intProductItemId] AS [intProductItemId], 
[Extent4].[intStorageId]     AS [intStorageId], 
[Extent4].[dAmount]          AS [dAmount], 
[Extent4].[mPrice]           AS [mPrice], 
[Extent4].[dtModified]       AS [dtModified], 
[Extent5].[pintId]           AS [pintId2], 
[Extent5].[nvcName]          AS [nvcName], 
[Extent5].[bIsDefault]       AS [bIsDefault] 
FROM   [Inventory] AS [Extent4] 
INNER JOIN [Storage] AS [Extent5] 
ON [Extent4].[intStorageId] = [Extent5].[pintId]) AS [Join3] 
ON [Extent1].[pintId] = [Join3].[intProductItemId] 
WHERE  [Extent2].[intCategoryId] = 8 /* @p__linq__0 */) AS [Project1] 
ORDER BY [Project1].[pintId1] ASC, 
[Project1].[pintId] ASC, 
[Project1].[pintId2] ASC, 
[Project1].[C1] ASC

对于数据库中的 7000 条记录和指定类别中的约 1000 条记录，此查询的执行时间约为 10 秒。看看这个就不足为奇了:

FROM [ProductItem] AS [Extent1]
INNER JOIN [Product] AS [Extent2]
ON [Extent1].[intProductId] = [Extent2].[pintId]
LEFT OUTER JOIN [Product] AS [Extent3]
ON [Extent1].[intProductId] = [Extent3].[pintId]
***LEFT OUTER JOIN (SELECT ....***

连接中的嵌套选择...可怕...我试图更改 LINQ 查询，但输出了相同的 SQL 查询。

我不能接受使用存储过程的解决方案，因为我使用的是 SQL Compact 数据库。

Answer 1

您正在执行 Include("Product").Include("Inventory").Include("Inventory.Storage") 并且您想知道为什么会获取这么多记录以及为什么会看到这样的记录一个大的 SQL 查询？请确保您了解 Include 方法的含义。如果您想要更简单的查询，请使用以下内容:

var res =
    from pi in objectSet
    where pi.Product.CategoryId == categoryId 
    select pi;

但是请注意，这可能会延迟加载 Products、Inventories 和 Storages，这可能会导致在您发送更多查询时迭代这些子集合。