Entity Framework classes, extending EF classes and adding custom properties, iQueryable and Get method

I'm at a loss as to how to title this, so if someone can rename this more appropriately, that would be appreciated.

I'm stuck as to how I c开发者_开发百科an go about populating custom properties of a partial entities class. Some examples

// partial class from EF base class - base class contains 
// properties such as commentID, comment, userID etc
// Comments.cs
public partial class Comment { 

    public int UpVotes { get; set; }
    public int DownVotes { get; set; }

    public int CurrentVotes()
    {
        return UpVotes - DownVotes;
    }

}

_

//CommentRepository.cs
//snip
public Comment GetItem(int id)
{
    Comment c = db.Comments.SingleOrDefault(x => x.CommentID == id);
    c.UpVotes = 0 //get UpVotes
    c.DownVotes = 0 // get DownVotes
    return c;
}

public IQueryable<Comment> GetAllCommentsByPage(int pageid)
{
}

public IQueryable<Comment> GetAllCommentsByPage(string slug)
{
}

public IQueryable<Comment> GetCommentSelection(int PageID, int Skip, int Take)
{
}

public int CountCommentByPage(int PageID)
{
}

In the old .Net 1.x days, I would have had the GetAllx methods select a list of CommentIDs, then populated a new List by using List.Add(GetItem(ID)).

In EF4, I want to do similar, but not lose out on the delayed execution of IQueryables.

In a couple of instances I have found it useful to stack these GetAllx methods in quick succession before doing a final .ToList() or similar to get the actual data.

Is there a sensible way for me to do what I hope is fairly simple and eluding me? I'd hate to have to change each method to return a static List of items that can be generated through the one GetItem method.

Thanks in advance.

----- edit -----

Okay, here's the solution I have currently:

public List<Comment> IQueryable2ToList(IQueryable<Comment> c)
{
    List<Comment> comments = new List<Comment>();
    List<int> ids = c.Select(x => x.CommentID).ToList();
    foreach (int id in ids) {
        comments.Add(GetComment(id));
    }
    return comments;
}

Which I call by doing:

List<Comment> comments = (new CommentRepository()).IQueryable2ToList(db.FindAllCommentsByPage(slug));

Which just seems a little dirty somehow...

Well, you can eliminate the n+1 selects:

public List<Comment> IQueryable2ToList(IQueryable<Comment> comments)
{
    List<Comment> comments = comments.ToList()
    foreach (Comment c in comments) {
        c.UpVotes = 0 //get UpVotes
        c.DownVotes = 0 // get DownVotes
    }
    return comments;
}

However, that's not what I'd do. Instead I'd make a presentation model and project:

public class CommentPresentation { 

    public int    CommentID { get; set; }
    public string WittyInsight { get; set; }
    public int    UpVotes { get; set; }
    public int    DownVotes { get; set; }

    public int CurrentVotes()
    {
        return UpVotes - DownVotes;
    }
}

public IQueryable<CommentPresentation> ToPresentation(IQueryable<Comment> comments)
{
    return from c in comments
           select new CommentPresentation
           {
               CommentId = c.CommentId,
               WittyInsight = c.WittyInsight,
               UpVotes = 0,
               DownVotes = 0
           };
}

If you want to assign something other than a constant, you may have to go through AsEnumerable(), so you'd want to do paging first. But this should get you started.