Ran into an interesting error. When using the following code:

EntityField fld = (EntityField)Courses.Fields[colname];
if (fld != null)   <<< compile time error here!!
{
 .... do things
}

I get the following error on the marked line...

The call is ambiguous between the following methods or properties: 'SD.LLBLGen.Pro.ORMSupportClasses.EntityField.operator !=(SD.LLBLGen.Pro.ORMSupportClasses.EntityField, System.Collections.ArrayList)' and 'SD.LLBLGen.Pro.ORMSupportClasses.EntityField.operator !=(SD.LLBLGen.Pro.ORMSupportClasses.EntityField, SD.LLBLGen.Pro.ORMSupportClasses.Expression)'

There are situations where the name passed in will not have a matching data field in the Courses entity. Since, without the null EntityField check, I get an exception complaining that the variable 'fld' is null, I thought the null check would work.

compare with DBNull.Value :) nooo, you don't need that. My mistake. I thought you were building a predicate. Indeed, casting to the interface solves it, see Walaa's answer .

Or if you are checking for the existance of such field you may use the following instead:

IEntityFieldCore fld = (EntityField)Courses.Fields[colname];
if (fld != null) <<< compile time error here!!
{
.... do things
}

Yep, that fixed it. Thanks!