What is right way to deal with "N+1" + Count problem? - entity-framework

Question

Supose the model as below:
class public Post
{
public int Id {get; set;}
public virtual ICollection<Comment> Comments {get;set;}
}
in the Posts/Index Page, I want to show a list of Post, with the Count of comments of each post (not total number of comments of all posts).
1: If I use
context.Posts.Include("Comments")
it will load the whole entity of all related commments , in fact I only need the Count of Comments.
2: If I get the count of each post one by one:
var commentCount = context.Entry(post)
.Collection(p => p.Comments)
.Query()
.Count();
that is a N+1 problem.
Any one knows the right way?
Thank you!

Answer 1

Do you need this for your presentation layer / view model? In such case create specialized ViewModel
public class PostListView
{
public Post Post { get; set; }
public int CommentsCount { get; set; }
}
And use query with projection:
var data = context.Posts
.Select(p => new PostListView
{
Post = p,
CommentsCount = p.Comments.Count()
});
And you are done. If you need it you can flatten your PostListView so that it contains Post's properties instead of Post entity.

Answer 2

What about something like this:
public class PostView
{
public String PostName { get; set; }
public Int32 PostCount { get; set; }
}
public static IEnumerable<PostView> GetPosts()
{
var context = new PostsEntities();
IQueryable<PostView> query = from posts in context.Posts
select new PostView
{
PostName = posts.Title,
PostCount = posts.PostComments.Count()
};
return query;
}
Then use something like this:
foreach (PostView post in GetPosts())
{
Console.WriteLine(String.Format("Post Name: {0}, Post Count: {1}", post.PostName, post.PostCount));
}
Should display the list as so:
Post name (12)
Post name (1)
Etc etc