I’m combining collection and would like to know the best method to remove duplicates.   I’m not going back to the database so distinct = true is not going to work for me.

Jeff

Well, here's a very interesting way if you're using .NET 3.5 using LINQ.

First, I added a comparer on my "Custom" class for the collection in Question.

namespace BusinessObjects
{
	public partial class EmployeesCollection : esEmployeesCollection, IEqualityComparer
	{
        #region IEqualityComparer Members

        bool IEqualityComparer.Equals(Employees x, Employees y)
        {
            return x.EmployeeID == y.EmployeeID;
        }

        int IEqualityComparer.GetHashCode(Employees obj)
        {
            return obj.EmployeeID.Value;
        }

        #endregion
    }
}

Now all I need to do is use the Union operator like this:

// Two sets of EmployeeID's
List<int> one = new List<int> { 1, 2, 3, 4 };
List<int> two = new List<int> { 3, 4, 5, 6 };

// Load the 1st one
EmployeesCollection oneColl = new EmployeesCollection();
oneColl.Query.Where(oneColl.Query.EmployeeID.In(one));
oneColl.Query.Load();

// Load the 2nd one
EmployeesCollection twoColl = new EmployeesCollection();
twoColl.Query.Where(twoColl.Query.EmployeeID.In(two));
twoColl.Query.Load();

// Use LINQ to return a Union (intersection), 
//
// NOTICE THAT THE SECOND PARAMETER TO UNION() METHOD IS THE
// COMPARER CLASS WHICH COULD BE ANY INSTANTIATED EmployeesCollection
IEnumerable uniqueQuery =
    oneColl.Union(twoColl, twoColl).OrderBy(e => e.EmployeeID);

// Did it work? Yes, it prints 1,2,3,4,5,6
foreach (Employees emp in uniqueQuery)
{
    Console.Write(emp.EmployeeID.Value.ToString());
}

// At this point I could create another collection and use Attach
// to create an entirely new collection
EmployeesCollection three = new EmployeesCollection();
foreach (Employees emp in uniqueQuery)
{
    three.AttachEntity(emp);
}

The alternative in .NET 2.0 would be to do something like this:

// Two sets of EmployeeID's
List<int> one = new List<int> { 1, 2, 3, 4 };
List<int> two = new List<int> { 3, 4, 5, 6 };

// Load the 1st one
EmployeesCollection oneColl = new EmployeesCollection();
oneColl.Query.Where(oneColl.Query.EmployeeID.In(one));
oneColl.Query.Load();

// Load the 2nd one
EmployeesCollection twoColl = new EmployeesCollection();
twoColl.Query.Where(twoColl.Query.EmployeeID.In(two));
twoColl.Query.Load();

foreach (Employees emp in twoColl)
{
    if (null == oneColl.FindByPrimaryKey(emp.EmployeeID.Value))
    {
        oneColl.AttachEntity(emp);
    }
}

foreach (Employees emp in oneColl)
{
    Console.Write(emp.EmployeeID.Value.ToString());
}

Hope those ideas help ...