例外的 ...包含路径前pression必须指向一个导航属性​​... 的基本抱怨 c.Comics.OrderBy 不是一个导航属性​​。 （这是一个合法的投诉，我想。）

其实这不是由EF支持的应用排序（和过滤）的预先加载语句（包含）。

那么，你该怎么办？

选项1：

排序在内存中完成装载后的实体：

  model.Page = db.Pages
    。凡（P =＆GT; p.PageId ==编号）
    .INCLUDE（P =＆GT; p.Series.Select（C =＆GT; c.Comics
                          。选择（COL =＆GT; col.Collection）））
    .SingleOrDefault（）;如果（model.Page！= NULL）
{
    的foreach（在model.Page.Series VAR系列）
        series.Comics = series.Comics.OrderBy（C =＆GT; c.ReadingOrder）.ToList（）;
}
 

丑陋，而是因为你是通过ID载入显然只有一个页对象是可能更快（LINQ到内存中的对象），比下面的选项（如系列和漫画集合是不是特别长）。

选项2：

细分查询零件其中混合渴望和explicite加载：

  model.Page = db.Pages
    。凡（P =＆GT; p.PageId ==编号）
    .INCLUDE（P =＆GT; P.系列车）//只收集系列包括
    .SingleOrDefault（）;如果（model.Page！= NULL）
{
    的foreach（在model.Page.Series VAR系列）
        db.Entry（系列）.Collection（S = GT; s.Comics）.Query（）
          .INCLUDE（C =＆GT; c.Collection）
          .OrderBy（C =＆GT; c.ReadingOrder）
          。加载（）; //一种新的数据库查询中循环每个系列
}
 

选项3：

投影？

Here和here是一些关于复的危害方式包括多个导航属性​​的链。它可以装载复制大量的数据。 包含确保您只有一个数据库往返，但可能在更多的转移数据的成本。 Explicite装载有多次往返，但在总的可能更少的数据。

（我知道，我给你这包括...选择...选择...选择...链条，但我怎么能知道你会带我认真:)。嗯，这取决于您的收藏嵌套的大小，它仍然是***的选择。）

I've got the following query:

model.Page = db.Pages
    .Where(p => p.PageId == Id)
    .Include(p => p.Series
                   .Select(c => c.Comics
                                 .Select(col => col.Collection)))
    .SingleOrDefault();

This works great, although I now need to order the Comics by a property called 'ReadingOrder'.

I've tried:

model.Page = db.Pages
    .Where(p => p.PageId == Id)
    .Include(p => p.Series.Select(c => c.Comics.OrderBy(o => o.ReadingOrder)
                          .Select(col => col.Collection)))
    .SingleOrDefault();

But this results in the following error:

The Include path expression must refer to a navigation property defined on the type. Use dotted paths for reference navigation properties and the Select operator for collection navigation properties. Parameter name: path

Any ideas what this error means?

Thanks in advance

EDIT:

My models:

public class Page
{
    public int PageId { get; set; }
    public string Title { get; set; }
    public ICollection<Series> Series { get; set; }
}

public class Series
{
    public int SeriesId { get; set; }
    public int PageId { get; set; }
    public string Title { get; set; }
    public Page Page { get; set; }
    public ICollection<Comic> Comics { get; set; }
}

public class Comic
{
    public int ComicId { get; set; }
    public string Title { get; set; }
    public int ReadingOrder { get; set; }
    public string Subtitle { get; set; }
    public int CollectionId { get; set; }
    public Collection Collection { get; set; }

}

public class Collection
{
    public int CollectionId { get; set; }
    public string Title { get; set; }
    public ICollection<Comic> Comics { get; set; }
}

The exception "...Include path expression must refer to a navigation property..." basically complains that c.Comics.OrderBy is not a navigation property. (It's a legitimate complaint, I think.)

Actually it's not supported by EF to apply sorting (and also filtering) in eager loading statements (Include).

So, what can you do?

Option 1:

Sort in memory after you have loaded the entity:

model.Page = db.Pages
    .Where(p => p.PageId == Id)
    .Include(p => p.Series.Select(c => c.Comics
                          .Select(col => col.Collection)))
    .SingleOrDefault();

if (model.Page != null)
{
    foreach (var series in model.Page.Series)
        series.Comics = series.Comics.OrderBy(c => c.ReadingOrder).ToList();
}

Ugly, but because you are loading apparently only a single Page object by id it's possibly faster (LINQ to Objects in memory) than the following options (if Series and Comics collections are not extraordinarily long).

Option 2:

Break down the query in parts which mix eager and explicite loading:

model.Page = db.Pages
    .Where(p => p.PageId == Id)
    .Include(p => p.Series) // only Series collection is included
    .SingleOrDefault();

if (model.Page != null)
{
    foreach (var series in model.Page.Series)
        db.Entry(series).Collection(s => s.Comics).Query()
          .Include(c => c.Collection)
          .OrderBy(c => c.ReadingOrder)
          .Load(); // one new DB query for each series in loop
}

Option 3:

Projection?

Here and here is by the way something about the dangers of complex Include chains of multiple navigation properties. It can load huge amounts of duplicated data. Include ensures that you only have one DB roundtrip but possibly at the cost of much more transfered data. Explicite loading has multiple roundtrips but with possibly less data in total.

(I know, I gave you this Include...Select...Select...Select... chain, but how could I know that you would take me serious :). Well, depending on the size of your nested collections it can still be the best option.)