实体框架5和SQL查询

I am facing serious performance issues... My query is supposed to filter Products with SQL directly in database. When I execute this code, it doesn't, and it returns all products and filters them in C#.

我正面临严重的性能问题……我的查询应该直接在数据库中使用SQL过滤产品。当我执行这段代码时，它没有，它返回所有产品并在c#中过滤它们。

MyContext context = new MyContext();

Func<Product, bool> query = (p => p.UPC.StartsWith("817"));

var products = context.Products.Where(query).Take(10);

I've noticed that the products variable is of type TakeIterator. When I change the code slightly, I get the filtering OK, but it forces me to put the query logic directly in the same method, which is what I want to avoid.

我注意到product变量是TakeIterator类型。当我稍微修改代码时，我得到了过滤，但是它迫使我将查询逻辑直接放在同一个方法中，这正是我想要避免的。

MyContext context = new MyContext();

var products = context.Products.Where(p => p.UPC.StartsWith("817")).Take(10);

This second version is of an undisclosed type by the Visual Studio debugger, but it shows as the query I am trying to end with, which is good!

第二个版本是由Visual Studio调试器提供的一种未公开的类型，但是它显示为我正在尝试使用的查询，这很好!

{SELECT TOP (10) 
[Extent1].[Id] AS [Id], 
[Extent1].[Brand] AS [Brand], 
[Extent1].[Description] AS [Description], 
[Extent1].[UPC] AS [UPC]
FROM [dbo].[Products] AS [Extent1]
WHERE [Extent1].[UPC] LIKE N'817%'}

I need to figure out how to get a Func passed as an argument and execute the query in the same fashion as the first C# code excerpt, but with optimisations of the second.

我需要弄清楚如何让Func作为一个参数传递，并以与第一个c#代码片段相同的方式执行查询，但是要对第二个代码进行优化。

1 个解决方案

#1

Try this instead:

试试这个:

MyContext context = new MyContext();

Expression<Func<Product, bool>> query = (p => p.UPC.StartsWith("817"));

var products = context.Products.Where(query).Take(10);

And see this question for reference on why:

请参考这个问题:

Why would you use Expression<Func<T>> rather than Func<T>?

为什么要用 >而不是Func ?

The accepted answer there is so complete that I don't dare try to explain it better!

公认的答案是如此完整，我不敢尝试更好地解释它!

#1