用Metaclass实现一个精简的ORM框架

 1 # -*- coding: utf-8 -*- 2 class Field(object): 3 ?4 ????def __init__(self, name, column_type): 5 ????????self.name = name 6 ????????self.column_type = column_type 7 ?8 ????def __str__(self): 9 ????????return ‘<%s:%s>‘ % (self.__class__.__name__, self.name)10 class StringField(Field):11 12 ????def __init__(self, name):13 ????????super(StringField, self).__init__(name, ‘varchar(100)‘)14 15 class IntegerField(Field):16 17 ????def __init__(self, name):18 ????????super(IntegerField, self).__init__(name, ‘bigint‘)19 class ModelMetaclass(type):20 21 ????def __new__(cls, name, bases, attrs):22 ????????if name==‘Model‘:23 ????????????return type.__new__(cls, name, bases, attrs)24 ????????print(‘Found model: %s‘ % name)25 ????????mappings = dict()26 ????????for k, v in attrs.items():27 ????????????if isinstance(v, Field):28 ????????????????print(‘Found mapping: %s ==> %s‘ % (k, v))29 ????????????????mappings[k] = v30 ????????for k in mappings.keys():31 ????????????attrs.pop(k)32 ????????attrs[‘__mappings__‘] = mappings # 保存属性和列的映射关系33 ????????attrs[‘__table__‘] = name # 假设表名和类名一致34 ????????return type.__new__(cls, name, bases, attrs)35 class Model(dict, metaclass=ModelMetaclass):36 37 ????def __init__(self, **kw):38 ????????super(Model, self).__init__(**kw)39 40 ????def __getattr__(self, key):41 ????????try:42 ????????????return self[key]43 ????????except KeyError:44 ????????????raise AttributeError(r"‘Model‘ object has no attribute ‘%s‘" % key)45 46 ????def __setattr__(self, key, value):47 ????????self[key] = value48 49 ????def save(self):50 ????????fields = []51 ????????params = []52 ????????args = []53 ????????for k, v in self.__mappings__.items():54 ????????????fields.append(v.name)55 ????????????params.append(‘?‘)56 ????????????args.append(getattr(self, k, None))57 ????????sql = ‘insert into %s (%s) values (%s)‘ % (self.__table__, ‘,‘.join(fields), ‘,‘.join(params))58 ????????print(‘SQL: %s‘ % sql)59 ????????print(‘ARGS: %s‘ % str(args))60 class User(Model):61 ????# 定义类的属性到列的映射：62 ????id = IntegerField(‘id‘)63 ????name = StringField(‘username‘)64 ????email = StringField(‘email‘)65 ????password = StringField(‘password‘)66 # 创建一个实例：67 u = User(id=12345, name=‘Michael‘, email=‘test@orm.org‘, password=‘my-pwd‘)68 # 保存到数据库：69 u.save()