WCF Data Services doesn't support many things

Question

I am using the March 2011 CTP2 of WCF Data Services and Entity Framework 4 Code First and am having a lot of problems with it. The problems I am having relate to "inner queries" not being supported.

For example, on my services side I have an Auction object, an Auction object can have attached to it 0 or more bids. Now, on my client side I wanted to execute this query to find the current highest bid (a being an Auction object).

a.Bids.OrderByDescending(b => b.Amount).First().Amount

Ignore the fact that this will fail if there are no bids. I get this error when I run this query

The expression [10007].Bids.OrderByDescending(b => b.Amount).First().Amount is not supported.

So I thought I would put this logic in the service side. From the client I call this method thus (again a is an Auction)

a => _auctionContext.GetHighestBid(a.Id).First().Amount

I again get an error

The expression value(UI.AuctionService.AuctionContext).GetHighestBid([10007].Id).First().Amount is not supported. 

My question is, why is this happening? Is it because of the version of WCF Data Services that I am using? Are these issues resolved in the latest release?

Thanks

Sachin

Edit

_auctionOrderings = new Dictionary<string, Func<IQueryable<Auction>, bool, IOrderedQueryable<Auction>>>
            {
                {"Ends", Utils.CreateOrderingFunc<Auction, DateTime?>(a => a.Ends)},
                {"CurrentPrice", Utils.CreateOrderingFunc<Auction, decimal>(a.Bids.OrderByDescending(b => b.Amount).First().Amount)},
                {"StartingPrice", Utils.CreateOrderingFunc<Auction, decimal>(a => a.StartingPrice)}
            };

public static Func<IQueryable<T>, bool, IOrderedQueryable<T>> CreateOrderingFunc<T, TKey>(Expression<Func<T, TKey>> keySelector)
        {
            return
                (source, ascending) =>
                ascending
                    ? source.OrderBy(keySelector)
                    : source.OrderByDescending(keySelector);
        }

Answer 1

Unfortunately not supported due to the nature of the protocol. Here's a list of things you can't do.

http://msdn.microsoft.com/en-us/library/ee622463.aspx

My recommendation is to create a service method to do what you want to do.