Does anybody have an idea how to use an enum in a linq expression ?

I have a simple class, with one attribute DocType - of an enum type DocumentType { Office, Private}

After creating the database, the ocl debugger knows everything about my DocumentType (knows all the values)

I've tried to form a linq expression like:

Class1 c = (from aClass in EcoSpace.PSQuery<Class1>()
                        where (aClass.TypeOfDocument == DocumentType.Private)
                        select aClass).FirstOrDefault();

When I try to run the application the following exception occurs:

System.InvalidOperationException was unhandled by user code
  Message="ECO LINQ: Unhandled nodetype Convert in UnaryExpression"
  Source="Eco.LinqExtender"
  StackTrace:
       at Eco.Linq.EcoQuery`1.WalkExpression(Expression parentexpression, Expression expression, OclEnvironment env, Dictionary`2 lambdaParameters) in e:\dev\fbuild\source\Eco\Eco.Linq\EcoQuery.cs:line 426
       at Eco.Linq.EcoQuery`1.WalkExpression(Expression parentexpression, Expression expression, OclEnvironment env, Dictionary`2 lambdaParameters) in e:\dev\fbuild\source\Eco\Eco.Linq\EcoQuery.cs:line 174
       at Eco.Linq.EcoQuery`1.WalkExpression(Expression parentexpression, Expression expression, OclEnvironment env, Dictionary`2 lambdaParameters) in e:\dev\fbuild\source\Eco\Eco.Linq\EcoQuery.cs:line 278
       at Eco.Linq.EcoQuery`1.WalkExpression(Expression parentexpression, Expression expression, OclEnvironment env, Dictionary`2 lambdaParameters) in e:\dev\fbuild\source\Eco\Eco.Linq\EcoQuery.cs:line 416
       at Eco.Linq.EcoQuery`1.HandleIterator(Expression parentexpression, OclEnvironment env, Dictionary`2 lambdaParameters, MethodCallExpression methodCallExp, String iteratorName, TBoldOCLIteratorSpecifier iteratorType) in e:\dev\fbuild\source\Eco\Eco.Linq\EcoQuery.cs:line 493
       at Eco.Linq.EcoQuery`1.WalkExpression(Expression parentexpression, Expression expression, OclEnvironment env, Dictionary`2 lambdaParameters) in e:\dev\fbuild\source\Eco\Eco.Linq\EcoQuery.cs:line 367
       at Eco.Linq.EcoQuery`1.CreateQuery[S](Expression expression) in e:\dev\fbuild\source\Eco\Eco.Linq\EcoQuery.cs:line 532
       at System.Linq.Queryable.Where[TSource](IQueryable`1 source, Expression`1 predicate)
       at EcoLinqBug.Form1.button1_Click(Object sender, EventArgs e) in C:\TestLab\EcoLinqBug\EcoLinqBug\Form1.cs:line 45
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativewindow.WndProc(Message& m)
       at System.Windows.Forms.Nativewindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
  InnerException:

Am I doing something wrong or is it a bug ?

What I can find on the net, implies that this is a valid expression, but I might miss something. Could someone please verify ?

Thnx - Per

I mostly added this post to remind you that .FirstOrDefault() only works if you add .ToArray() before it (more info).

Rick Weyrauch

My example works fine with FirstOrDefault() (odd, if it did not work for you), because if the query return an empty result (ie. null) the call throws an exception.

Per

[Test]
public void FirstOrDefault()
{
  var es = new NotDerivedSettableEcoSpace { Active = true };
  var class3 = (from c3 in es.PSQuery<Class3>() where c3.Option == 100 select c3).ToArray().FirstOrDefault();
  Assert.That(class3, Is.Not.Null);
  class3 = (from c3 in es.PSQuery<Class3>() where c3.Option == 100 select c3).FirstOrDefault();
  Assert.That(class3, Is.Not.Null);
}

if (ecospace.PSQuery<Vintage>().FirstOrDefault(v => v.Year == year) != null)
  throw new ArgumentOutOfRangeException("year", string.Format("Unable to create new vintage for {0} - Duplicate!", year));

If I call this 3 times in a row, with UpdateDatabase() in between of course, it never tosses the exception.

if ( ((IEnumerable<Vintage> )ecospace.PSQuery<Vintage>().Where(v => v.Year == year)).FirstOrDefault() != null)
  throw new ArgumentOutOfRangeException("year", string.Format("Unable to create new vintage for {0} - Duplicate!", year));

I beleive this is true for all of the Element Operators and Aggregation Operators but I do not know that for sure.

What are the chances that you are using a cast to IEnumerable as part of your route to FirstOrDefault()?

Yep, thats it. I'd tried a lot of examples from microsoft's website, and one of those examples did indeed contain a type cast to IEnumerable. Other places in the code where I'd tried the FirstOrDefault(), failed miserably!

Lesson learned - When reading my own code, be more careful 

thnx for your insight. Per