orm_without_metaclass.py

class Field(object):
    def __init__(self, name, column_type):
        self.name = name
        self.column_type = column_type

    def __str__(self):
        return '<%s:%s>' % (self.__class__.__name__, self.name)


class StringField(Field):
    def __init__(self, name):
        super(StringField, self).__init__(name, 'varchar(100)')


class IntegerField(Field):
    def __init__(self, name):
        super(IntegerField, self).__init__(name, 'bigint')


class Model(dict):
    __db__ = 'db_name'

    def __new__(cls, **kws):

        cls.__table__ = cls.__name__
        cls.__mappings__ = {k: getattr(cls, k) for k in dir(
            cls) if isinstance(getattr(cls, k), Field)}

        return super().__new__(cls, **kws)

    def __init__(self, **kws):
        for k in self.__mappings__.keys():
            setattr(self, k, kws.get(k))

        _kws = {k: v for k, v in kws.items() if k in self.__mappings__.keys()}
        super().__init__(**_kws)

    def __setattr__(self, key, value):

        print('set: ', key, '--->', value)
        if key not in self.__mappings__.keys():
            raise AttributeError(r'unavailable key: %s' % key)
        self[key] = value
        super().__setattr__(key, value)

    def save(self):
        fields = []
        params = []
        args = []
        for k, v in self.__mappings__.items():
            fields.append(v.name)
            params.append('?')
            args.append(getattr(self, k, None))

        sql = 'insert into %s (%s) values (%s)' % (
            self.__table__, ','.join(fields), ','.join(params))
        print('SQL: %s' % sql)
        print('ARGS: %s' % str(args))


class User(Model):

    id = IntegerField('id')
    name = StringField('username')
    email = StringField('email')
    password = StringField('password')


class SubUser(User):

    nickname = StringField('nickname')


if __name__ == '__main__':

    u = User(id=123, name='Michael', email='test@orm.org', password='my-pwd')
    u.save()