RIA DomainService IQueryable - Select - c#-4.0

Question

Following a couple different tutorials, I've been trying to build a "Silverlight Business Application" against a database I've created. I've found I have two problems. The one I'm asking about here is how to filter the query.
The query that is built in the DomainService is when using the VS2010 template is:
[EnableClientAccess]
public class ChargesService : LinqToEntitiesDomainService<ChargesEntities>
{
public IQueryable<tblChargeCode> GetCharges()
{
return ObjectContext.tblChargeCodes.OrderBy(e => e.Chrgs_Code_01).Take(10);
}
}
I'm trying to create another query against the same ObjectContext.tblChargeCodes. Pulling the entire table (30 columns by ~7k rows) creates a timeout error.
I can't figure out how to do a select. I want to select Charge_Codes_01 and Bill_Description with a "starts with" type functionality (dynamic drop down search functionality). I've tried different variations of this without success. Something just isn't clicking in my brain.
public IQueryable<tblChargeCode> SearchCharges(string num)
{
var min = System.Convert.ToInt32(num.PadRight(7, '0'));
var max = System.Convert.ToInt32(num.PadRight(7, '9'));
return ObjectContext.tblChargeCodes
.Select(e => e.Chrgs_Code_01, e.Chrgs_Code_01_Desc)
.Where(e => e.Chrgs_Code_01 >= min && e.Chrgs_Code_01 <= max)
.OrderBy(e => e.Chrgs_Code_01)
.Take(10);
}

Answer 1

(sorry for my bad english)
The problem with you code is the "Select" - your method signature says that it must return a IQueryable of tblChargeCode, so you cannot return a projection. Here is two ways you can write your query:
In the server:
public IQueryable<tblChargeCode> SearchCharges(int min, int max, string description)
{
return ObjectContext.tblChargeCodes
.Where(e => e.Chrgs_Code_01 >= min && e.Chrgs_Code_01 <= max)
.Where(e => e.Bill_Description.StartsWith(description))
.OrderBy(e => e.Chrgs_Code_01)
.Take(10);
}
And call it on the client:
context.Load(context.SearchChargesQuery(0, 9999999, "Bill"), (op) =>
{
//op.Entities has your entities loaded
}, null);
Or you can just leave the query on the server:
public IQueryable<tblChargeCode> GetCharges()
{
return ObjectContext.tblChargeCodes.OrderBy(e => e.Chrgs_Code_01);
}
And call it from the client (it will filter on the server)
context.Load(context.GetChargesQuery().Where(e => e.Chrgs_Code_01 >= 0 && e.Chrgs_Code_01 <= 9999999)
.Where(e => e.Bill_Description.StartsWith("Bill"))
.OrderBy(e => e.Chrgs_Code_01)
.Take(10), (op) =>
{
//op.Entities has your entities loaded
}, null);
You also can use "Contains" instead of "StartsWith" in your query.