Question

In a Win7 app, I am trying to update several fields in an ADO.NET database table called “Channel”, with an EntitySetMapping Name of “Channels”, using EntityClient in the EF to access SqlServerCe 3.5 (IPManager_DBEntities).

With the VS 2010 IDE, the code compiles fine and Intellisense has no complaints. The format of the Channel datatable is referenced at the bottom as the various fields in a row (selected by Channel “Number”) need to be updated with information passed to it from code which is not shown for the sake of simplicity. Nothing I have Googled during the past several days has solved my Type Casting dilemma. Using LINQ, I get this RunTime Exception:

“Unable to cast object of type ‘System.Data.Objects.ObjectQuery`1 [Manager.Data.Channel]’ to type ‘Manager.Data.Channel'”.

    // Update channel status with information parsed from the data packet.
    using (IPManager_DBEntities context = new IPManager_DBEntities())
    {
        Channel thisChannelRow = (Channel)(from CE
                                             in context.Channels
                                          where CE. Number == int.Parse(IDLine[2])
                                         select CE);

        // Throwing exception after setting up this query:
        //   "Unable to cast object of type 'System.Data.Objects.ObjectQuery`1
        //   [Manager.Data.Channel]' to type 'Manager.Data.Channel'"
        //  During debug sessions, "thisChannelRow" is null as a result.

        MessageBox.Show("thisChannelRow. Channel = " + thisChannelRow.Number );

            ThisChannel.StatusID = int.Parse(IDLine[5]);
            ThisChannel.Cycle = int.Parse(IDLine[4]);
            ThisChannel.Modified = DateTime.Now;
            context.SaveChanges();
     }

I hope someone has a solution to help me through this predicament.

Answer 1

The LINQ query is returning an object of a type descendant from IEnumerable<T>, not Channel, even if there is just one item in the sequence. To get the actual item, use FirstOrDefault:

Channel thisChannelRow = (Channel)(from CE
                                   in context.Channels
                                   where CE. Number == int.Parse(IDLine[2])
                                   select CE).FirstOrDefault();

Or First, Single, or SingleOrDefault if any of those are a better fit.