InvalidCastException when getting first result from LINQ query

Greetings!

I am a complete newbie at LINQ. I am trying to get my first simple little application using it to run. It's built in Visual Studio 2008, using DevArt's LinqConnect product to talk to a PostgreSQL database. Here's the function:

Code:

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                private void dgvCharges_CellClick(object sender, DataGridViewCellEventArgs e)
                {
                        long chargeNumber = Convert.ToInt32(dgvCharges[e.ColumnIndex, e.RowIndex].Value);
                        var oneChargeSet = from charge in m_context.Charges
                                                        where charge.Charge1 == chargeNumber
                                                        select charge;
                        int chargeCount = oneChargeSet.Count();
                        var oneCharge = oneChargeSet.First();                     
                }

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In the debugger, I see that chargeCount is 1, as expected. I believe that the First() function should return an object that contains all of the data members of the charge table in the database: Charge1, BuiltDate, LoadedDate, Cycle, and everything else. This code compiles and starts nicely. But when I invoke the First() method, I get an InvalidCastException. I get the same expression when I try to give First an explicit type:

Code:

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                private void dgvCharges_CellClick(object sender, DataGridViewCellEventArgs e)
                {
                        long chargeNumber = Convert.ToInt32(dgvCharges[e.ColumnIndex, e.RowIndex].Value);
                        var oneChargeSet = from charge in m_context.Charges
                                                        where charge.Charge1 == chargeNumber
                                                        select charge;
                        int chargeCount = oneChargeSet.Count();
                        var oneCharge = oneChargeSet.First<AnnealContext.Charge>();
                }

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Obviously, I don't understand something basic about LINQ. How do I get this to work?

Thanks very much!

RobR

Update: If I do not specify an explicit list of fields, I can pass the query object into a data view control, and the control will display the contents of the table as expected. If I want to use the results of the query in my application, I can include an explicit list of fields to return, and it will work. That's probably a good idea anyway. I remain curious, though, why I can't get the simple first form to work.

Here's what's working for me:

Code:

---


                        var oneChargeSet = from charge in m_context.Charges
                                                        where charge.Charge1 == chargeNumber
                                                        select new
                                                        {
                                                                charge.Charge1,
                                                                charge.Loaded_Date,
                                                                charge.Purge_Date,
                                                                charge.Standby_Date,
                                                                charge.Fire_Date,
                                                                charge.Off_Date,
                                                                charge.Cool_Date,
                                                                charge.Cold_Date,
                                                                charge.Unloaded_Date
                                                        };
                       
                        var oneCharge = oneChargeSet.First();

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