'Add the given list of model field names to the set of fields to
exclude from loading from the database when automatic column selection
is done. The new field names are added to any existing field names that
are deferred (or removed from any existing field names that are marked
as the only ones for immediate loading).'

def add_deferred_loading(self, field_names):

    (existing, defer) = self.deferred_loading
    if defer:
        self.deferred_loading = (existing.union(field_names), True)
    else:
        self.deferred_loading = (existing.difference(field_names), False)
