实体框架 - 加载相关实体 [英] Entity Framework - Eager loading related entities

问题描述

我正在使用MVC的Entity Framework 4，并且需要确保在我的视图中使用的任何引用的实体在控制器方法返回之前被加载，否则视图会吐出可怕的：

ObjectContext实例已被处理，不能再用于需要连接的操作。

从上下文中直接选择时，我可以使用 Include（string）方法强制将其包含在生成的SQL查询中： / p>

  var sellerers = context.Sellers.Include（recommendations.User）ToList（）; 
  

但是，如果我有（例如）一个接受一个实体并需要所有项目的辅助方法被加载，没有包含方法可用。

  void Test卖家）
 {
 //确保所有建议及其用户加载
} 
  

蛮力的方法是循环通过它们：

  foreach（在卖家推荐的推荐）
 recommendations.User.ToString（）; //只是强制加载
  

如果我有100个建议，这将在后面创建101个SQL查询-scenes。理想情况下，我想要一种方法/方法，只需单独访问SQL即可加载所有建议和用户对象。 p>

显示我的钱。

编辑我不太在意讨论是否这是一个好或坏的建筑。为了这个问题我简化了我的场景。你可以用EF API做什么吗？

编辑2

Ladislav的编辑提供了一种新的方法的希望，但是似乎我不在那里。

我可以通过以下方式实现我想要的：

  context.Sellers.Include（recommendations.User）。Single（s => s.Id == seller.Id）; 
  

此方法无法使用 LoadProperty ...

  context.LoadProperty（seller，recommendations.User）; 
  

...因为失败，错误...

无法找到指定的导航属性Recommendation.User。

如果你没有上下文的引用，这些方法是有效的。

解决方案

这是一个旧问题，但是在EF6中可以在此上的实体上实现加载依赖对象：

  context.Entry（seller）.Collection（s => s.Recommendations）.Query（）。Include（r => r.User）） 。加载（）; 
  

这将加载所有建议及其相关用户针对给定的卖家

I'm using Entity Framework 4 with MVC and need to ensure any referenced entities I want to use in my view have been loaded before the controller method returns, otherwise the view spits out the dreaded:

The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

When selecting straight from the context, I can just use the Include(string) method to force them to be included in the generated SQL query:

var sellers = context.Sellers.Include("Recommendations.User").ToList();

However, if I have (for example) a helper method that accepts an entity and needs all items to be loaded, there's no Include method available.

void Test(Seller seller)
{
    // ensure all recommendations and their users are loaded
}

The brute force approach is to loop through them:

foreach (var recommendation in seller.Recommendations)
    recommendation.User.ToString(); // just force a load

If I have 100 recommendations, this will create 101 SQL queries behind-the-scenes. Ideally I want a method/approach that loads all Recommendation AND User objects with only a single trip to SQL.

Show me the money.

EDIT I'm not really interested in discussing whether this is a good or bad architecture. I've simplified my scenario for the sake of the question. Can you do what I'm asking with the EF API?

EDIT 2

Ladislav's edit offered hope of a new approach, but it seems I'm not quite there.

I can achieve what I want via this:

context.Sellers.Include("Recommendations.User").Single(s => s.Id == seller.Id);

This approach doesn't work using LoadProperty...

context.LoadProperty(seller, "Recommendations.User");

...as it fails with the error...

The specified navigation property Recommendations.User could not be found.

Neither of these approaches work if you don't have a reference to the context.

解决方案

This is an old question, but in EF6 you can accomplish loading dependent objects on an entity like this:

context.Entry(seller).Collection(s => s.Recommendations).Query().Include(r => r.User)).Load();

That would load all Recommendations and their related Users for the given seller

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