基于抽象的实体与预先加载嵌套导航问题（EF CTP5） [英] Problem with Eager Loading Nested Navigation Based on Abstract Entity (EF CTP5)

问题描述

我看起来像这样我的EF模型的部分内容：

I a portion of my EF model that looks like this:

摘要：

• 地点有许多文章


• 邮政是一个摘要类


• 讨论的导出从发表


• 讨论许多注释

• Location has many Posts
• Post is an abstract class
• Discussion derives from Post
• Discussions have many Comments

现在，查询我试图实现的：

Now, the query i'm trying to achieve:

获取有关地点标识1234，包括与相关的任何讨论和评论信息这些讨论

我能得到讨论，这样的评论：

I can get discussions and the comments like this:

var discussions = ctx.Posts
                     .OfType<Discussion>()
                     .Include(x => x.Comments)
                     .ToList();

但我似乎无法得到它的基础上的文章导航。在位置实体

我试过这样：

var locationWithDiscussionsAndComments = ctx
                    .Locations
                    .Include(x => x.Posts
                                   .OfType<Discussion>()
                                   .Select(y => y.Comments))
                    .SingleOrDefault();

其中编译，但我得到的错误：

Which compiles, but i get the error:

System.ArgumentException：include路径表达式必须是指由实体定义的属性，也可选择嵌套的属性或调用来选择。
参数名称：路径

System.ArgumentException: The include path expression must refer to a property defined by the entity, optionally also with nested properties or calls to Select. Parameter name: path

任何想法？我大概可以走倒退，从文章：

Any ideas? I could probably go "backwards" from the Posts:

var locationWithDiscussionsAndComments = ctx
                   .Posts
                   .Include(x => x.Location)
                   .OfType<Discussion>()
                   .Include(x => x.Comments)
                   .Where(x => x.LocationId == 1234)
                   .Select(x => x.Location)
                   .ToList();

但是，这既是毛茸茸和语义错误的，我库而言（我不应该去通过岗位信息库，以获取有关位置的信息）。

But that is both hairy and semantically wrong in terms of my repositories (i shouldn't have to go through a post repository to get information about a location).

任何想法？

修改

因此，有一个更大的思考后，我意识到， OfType< T> 是一个过滤器操作。正如我们所知，EF不支持与预先加载过滤。唯一的选择是检索家居或使用匿名类型的投影。

So after having a bigger think about it, i realized that OfType<T> is a filter operation. As as we know, EF does not support filtering with eager loading. The only options are retrieving everything, or using anonymous type projection.

没有办法，我可以检索的一切，因为有太多的元数据参与其中。所以我试图匿名类型的投影

No way i can retrieve everything, as there is far too much meta data involved. So i'm attempting the anonymous type projection.

推荐答案

新的查询的方法可以帮助你：

The new Query method might help you:

var location = context.Locations.SingleOrDefault();

context.Entry(location)
       .Collection(l => l.Posts)
       .Query()
       .OfType<Discussion>()
       .Load();

结果

我们可以添加一个新的 LoadProperty 的泛型方法到库< T> 类它利用这个新的查询方法：

We can add a new LoadProperty generic method to the Repository<T> class that leverages this new QUery method:

public void LoadProperty<TElement>(T entity, 
        Expression<Func<T, ICollection<TElement>>> navigationProperty,
        Expression<Func<TElement, bool>> predicate) where TElement : class
{
    _context.Set<T>().Attach(entity);

    _context.Entry(entity)         
            .Collection(navigationProperty)
            .Query()
            .Where(predicate)
            .Load();
}

使用LoadProperty方法：

Using the LoadProperty method:

Location location = _locationRepository.Find(1);
_locationRepository.LoadProperty(location, l => l.Posts, p => p is Discussion);

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