how to use lazy choice in model

In my project, I have a dictionary in database,  i want to get choices that used in model from this dictionary,  I defined  something as follows, expect it loaded lazy:

class DictionaryChoices(object):

    def __getattr__(self, item):
        cursor = connections['default'].cursor()
        cursor.execute("SELECT c_item_id,c_item_name FROM tblcommon_base_data where c_type=%s", [item])
        row = cursor.fetchall()
        return row


class LazyDictionary(LazyObject):
    def _setup(self):
        self._wrapped = DictionaryChoices()


def get_dictionary_by_types(types):
    obj = LazyDictionary()
    result = getattr(obj, types)
    return result


def get_dictionary_string_by_types(types):
    obj = LazyDictionary()
    result = getattr(obj, types)
    string_result = tuple([(str(i[0]), i[1]) for i in result])
    return string_result

In other models, i use it as follows:

CREDENTIALS_TYPE = get_dictionary_by_types('credentials_type')

credentials_type = models.SmallIntegerField(choices=CREDENTIALS_TYPE, default=1, db_column='c_credentials_type')

it works, but it not lazy,  when a insert new item to the choices , it can not load except reboot the server, maybe i can use foreignkey, but i want to know how to make it work like lazy choices, thanks for help!

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