private void FindDroppedColumns(
Tuple <IEntityType, IEntityType> tablePair,
IEnumerable <Tuple <IProperty, IProperty> > columnPairs)
{
_operations.AddRange(
tablePair.Item1.Properties
.Except(columnPairs.Select(pair => pair.Item1))
.Select(c => OperationFactory.DropColumnOperation(c)));
}