RIA services how do I return a single column?

I have a autocompletebox that is used to select a destination for a car booking program. For the itemssource of the autocomplete box I am trying to set it to all the previous destinations ent开发者_运维知识库ered. The problem is that I can't work out how to return a single column 'Destination' of distinct destination values from my Booking class, e.g.

        var query = from bk in ObjectContext.Bookings select new DestinationDTO { Destination = bk.Destination };
        return query.Distinct();

. I have tried creating a shared DestinationDTO class to return just the single column but can't work out how to get this to inherit from Entity!!

Any ideas?

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You need to have a property with a [Key] attribute in your DestinationDTO class. Then RIA services will be able to generate a corresponding class on the client side.

public class DestinationDTO 
{
    [Key]
    public Guid Id { get; set; }

    public string Destination { get; set; }
}

Then just do this:

var query = from bk in ObjectContext.Bookings 
    select new DestinationDTO { Destination = bk.Destination, Id = Guid.NewGuid() };
    return query.Distinct();