def _get_or_update_model(case_update, xform, case_db):
"""
Gets or updates an existing case, based on a block of data in a
submitted form. Doesn't save anything.
"""
case = case_db.get(case_update.id)
if case is None:
case = ActionsUpdateStrategy.case_from_case_update(case_update, xform)
case_db.set(case['_id'], case)
return case
else:
ActionsUpdateStrategy(case).update_from_case_update(case_update, xform, case_db.get_cached_forms())
return case
