实体框架 - 包含在子查询中？ - 第2部分 [英] Entity Framework - Include in sub query? - Part 2

问题描述

我不知道这是否是正确的事情，我相信有人会告诉我，如果不是。

我问了一个问题（<一个href =https://stackoverflow.com/questions/1662760/entity-framework-include-in-sub-query>实体框架 - 包含在子查询中）今天晚上，这是非常回答的好了，解决了我的问题。但是，我认为可能会有一个更好的方法，所以我要重新提出这个问题，但是略有不同。

我有3个表： / p>

餐厅1 ..... M MenuCategory 1 ..... M MenuItem
我有一个看起来像这样的L2E查询：

Restaurant = context.Restaurant
.Include（r => r.MenuCategory）
.FirstOrDefault（r => r.RestaurantId == resaurantId）;
哪些工作在某种程度上，但它只能预先加载菜单类别。

我真正想要做的是这样的： p>

  Restaurant = context.Restaurant 
 .Include（r => r.MenuCategory）
 .Include（r = r.MenuCategory.MenuItems）
 .FirstOrDefault（r => r.RestaurantId == resaurantId）; 
  

但显然这不可用，因为r.MenuCategory是一个可枚举的

...的工作是使用标准符号：

  context.Restaurant.Include （ MenuCategory.MenuItems）; 
  

...但这不是强类型的。这个问题是关于发现一个强类型答案

这是目前的扩展方法：

  public static ObjectQuery< T>包含< T>（此ObjectQuery< T>查询，表达式< Func< T，对象>>路径）
 {
 //检索成员路径：
列表< PropertyInfo> members = new List< PropertyInfo>（）; 
 EntityFrameworkHelper.CollectRelationalMembers（path，members）; 
 
 //构建字符串路径：
 StringBuilder sb = new StringBuilder（）; 
 string separator =; 
 foreach（成员中的MemberInfo成员）
 {
 sb.Append（separator）; 
 sb.Append（member.Name）; 
 separator =。; 
} 
 
 //应用Include：
 return query.Include（sb.ToString（））; 
} 
  

这可以如何适应以允许强类型的形式：

  context.Restaurant.Include（MenuCategory.MenuItems）; 
  

解决方案

我有一个提示，正是这样：提示28 - How实施一个热切的负载策略

使用一个漂亮的技巧我认为。

Alex

I'm not sure if this is the right thing to do, I'm sure someone will tell me if it's not.

I asked a question (Entity Framework - Include in sub query?) earlier this evening, which was answered very well and has solved my problem. But, I think there could be a better way, so I'm going to re-ask the question, but slightly differently.

Let's say I have 3 tables:

Restaurant 1.....M MenuCategory 1.....M MenuItem I have a L2E query that looks something like this:

Restaurant = context.Restaurant .Include(r => r.MenuCategory) .FirstOrDefault(r => r.RestaurantId == resaurantId); Which works to some extent, but it only pre-loads the menu categories.

What I really want to be able to do is something like:

Restaurant = context.Restaurant
.Include(r => r.MenuCategory)
.Include(r => r.MenuCategory.MenuItems)
.FirstOrDefault(r => r.RestaurantId == resaurantId);

But clearly this isn't available as r.MenuCategory is an enumerable

...the work around is to use the standard notation:

context.Restaurant.Include("MenuCategory.MenuItems");

...but this is not strongly typed. This question is about finding a strongly typed answer

This is the current extension method:

public static ObjectQuery<T> Include<T>(this ObjectQuery<T> query, Expression<Func<T, object>> path)
{
    // Retrieve member path:  
    List<PropertyInfo> members = new List<PropertyInfo>();
    EntityFrameworkHelper.CollectRelationalMembers(path, members);

    // Build string path:  
    StringBuilder sb = new StringBuilder();
    string separator = "";
    foreach (MemberInfo member in members)
    {
        sb.Append(separator);
        sb.Append(member.Name);
        separator = ".";
    }

    // Apply Include:  
    return query.Include(sb.ToString());
}

How could this be adapted to allow a strongly typed form of:

context.Restaurant.Include("MenuCategory.MenuItems");

解决方案

I have a Tip that allows exactly this: Tip 28 - How to implement an eager load strategy

Uses a nifty trick I think.

Alex

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