如何LINQ前$ P $与pssion语法工作包括（）进行预先加载 [英] How does LINQ expression syntax work with Include() for eager loading

问题描述

我有一个查询下面，但我想执行的include（）跃跃欲试负载性能。操作有一个导航属性​​，用户（Action.User）

I have a query below, but I want to perform an Include() to eager load properties. Actions has a navigation property, User (Action.User)

1）我的基本的查询：

1) My basic query:

from a in Actions
join u in Users on a.UserId equals u.UserId
select a

2）第一次尝试：

2) First attempt:

from a in Actions.Include("User")
join u in Users on a.UserId equals u.UserId
select a

但Action.User是的不可以填充。

3）尽量渴望负荷用户进入查询之外在行动导航属性：

3) Try to eager load 'User' into the navigation property in action outside of query:

(from a in Actions
join u in Users on a.UserId equals u.UserId    
select a).Include("User")

在LINQPad试图包含的我得到一个错误：

In LINQPad trying Include's I get an error:

System.Linq.IQueryable'不包含'包含'的定义，并没有扩展方法包含接受型System.Linq.IQueryable'的第一个参数可以发现（preSS F4添加using指令或程序集的引用）

'System.Linq.IQueryable' does not contain a definition for 'Include' and no extension method 'Include' accepting a first argument of type 'System.Linq.IQueryable' could be found (press F4 to add a using directive or assembly reference)

我想这是因为LINQ不支持包括（）。

I think this is because LINQ doesn't support Include().

于是，我就在VS;查询2运行，但返回无人居住的用户属性。
问题3似乎扩展方法不存在，尽管它不行动本身不存在的查询。

So I tried in VS; query 2 runs, but returns unpopulated User property. Query 3 the extension method does not seem to exist, although it does exist on Action itself without the query.

推荐答案

我想通了，感谢反正建议。
解决的办法是这样做（第2次尝试在我的问题）：

I figured it out, thanks for the suggestions anyway. The solution is to do this (2nd attempt in my question):

var qry = (from a in Actions
join u in Users on a.UserId equals u.UserId    
select a).Include("User")

智能感知之所以没有表现出包括后查询是因为我需要使用以下内容：

The reason intellisense didn't show Include after the query was because I needed the following using:

using System.Data.Entity;

一切正常这样做。

Everything worked fine doing this.

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