How to limit number of related data with Include

问题

class Cat
{
   public int CatID;
   public string Name;
   public ICollection<Post> Posts;
}
class Post
{
   public int PostID;
   public string Name

   public int CatID;
   public virtual Cat Parent;
}

And I want to load all the Catergories with their Posts so:

var cats = context.Cat.Include(c => c.Posts);

Now I want to limit the number of Posts that are returned, can someone show mw how to do that?

I'm using EntityFramework 4.3.1

回答1:

It is not possible with eager loading (Include) - eager loading returns always all related data. You must use projections to anonymous or new type (you cannot use your existing mapped entities):

var cats = context.Cat.Select(c => new 
{ 
    Category = c, 
    Posts = c.Posts.OrderBy(p => p.Name).Take(10) 
});

回答2:

You cannot use projections with Include() method but note that in the query below you can limit the number of Categories returned using Name field of Posts.

using (var context = new YourContext())
{
    var categories = from c in context.Categories.Include("Posts")
                    where c.Posts.Any((p)=>p.Name == "Linq")
                    select c;
}

Also you can do something like this:

context.Categories
       .Select(c => new { 
                         Category = c, 
                         Posts = c.Posts.Where(p => p.Name == "Linq") 
       }).AsEnumerable()
       .Select(cp => cp.Category);

Hope it helps.

来源：https://stackoverflow.com/questions/9545428/how-to-limit-number-of-related-data-with-include