LINQ 表达式语法如何与 Include() 一起用于预先加载 [英] How does LINQ expression syntax work with Include() for eager loading

问题描述

我在下面有一个查询，但我想执行 Include() 来急切加载属性.Actions 有一个导航属性，User(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) 我的基本查询:

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

2) 第一次尝试:

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

但 Action.User 未填充.

But Action.User is not populated.

3) 尝试在查询之外的操作中急切地将用户"加载到导航属性中:

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")

在尝试包含的 LINQPad 中，我收到一个错误:

In LINQPad trying Include's I get an error:

System.Linq.IQueryable"不包含Include"的定义，并且找不到接受System.Linq.IQueryable"类型的第一个参数的扩展方法Include"(按 F4 添加 using 指令或汇编参考)

'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)

我认为这是因为 LINQ 不支持 Include().

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

所以我在VS中尝试过；查询 2 运行，但返回未填充的用户属性.Query 3 的扩展方法似乎不存在，尽管它确实存在于没有查询的 Action 本身.

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，无论如何感谢您的建议.解决方案是这样做(我的问题中的第二次尝试):

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")

intellisense 在查询后没有显示 Include 的原因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;

这样做一切正常.

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