Return the result of joining two tables in Silverlight 4.0 - visual-studio-2010

Question

Main Code:
DomainServiceAccountManager d = new DomainServiceAccountManager();
EntityQuery<ListBuy> q = d.GetListMemberBuyQuery();
LoadOperation<ListBuy> l = d.Load(q);
DGListBuy.ItemsSource = l.Entities;
The code:
public IQueryable<ListBuy> GetListMemberBuy()
{
var membuy =
from mem in this.ObjectContext.Members
from b in this.ObjectContext.Buys.Where(b => b.ID_member == mem.ID)
.OrderByDescending(b => b.ID)
.DefaultIfEmpty()
select new { b.ID, mem.Name, b.Money, b.Tarikh };
return membuy;
}
I get the following message:
Cannot implicitly convert type 'System.Linq.IQueryable<AnonymousType#1>' to 'System.Linq.IQueryable<AccountManager.Web.ListBuy>'. An explicit conversion exists (are you missing a cast?)

Answer 1

You method GetListMemberBuy actually returns an IQueryable of anonymous type instead of an IQueryable of type ListBuy. These are not identical, hence the (compile time?) error.
I can only assume that ListBuy also exists in the database, but if so, then you can remove the anonymous type.
public IQueryable<ListBuy> GetListMemberBuy()
{
var membuy =
from mem in this.ObjectContext.Members
from b in this.ObjectContext.Buys.Where(b => b.ID_member == mem.ID)
.OrderByDescending(b => b.ID)
.DefaultIfEmpty()
select new ListBuy() { ID = b.ID, Name = mem.Name, Money = b.Money, Tarikh = b.Tarikh }; // <-- new ListBuy() !!
return membuy;
}
If ListBuy does not exist in the database, then you cannot return an IQueryable. Maybe this will work.
public IEnumerable<ListBuy> GetListMemberBuy()
{
var membuy =
from mem in this.ObjectContext.Members
from b in this.ObjectContext.Buys.Where(b => b.ID_member == mem.ID)
.OrderByDescending(b => b.ID)
.DefaultIfEmpty()
select new { b.ID, mem.Name, b.Money, b.Tarikh };
return membuy
.AsEnumerable()
.Select(b => new ListBuy() {
ID = b.ID, Name = b.Name, Money = b.Money, Tarikh = b.Tarikh
});
}
All this is a bit speculation since you didn't include the ListBuy class definition in your question.