class Field(object):def __init__(self, name, colum_type):self.name = nameself.colum_type = colum_typedef __str__(self):return "<%s:%s>" % (self.__class__.__name__, self.name)class IntegerField(Field):def __init__(self, name):super(IntegerField, self).__init__(name, "bigint")class StringField(Field):def __init__(self, name):super(StringField, self).__init__(name, "varchar(100)")class ModelMetaclass(type):def __new__(cls, name, bases, attrs):if name=='Model':return type.__new__(cls, name, bases, attrs)#将attrs中为数据库类型的变量转移到__mapping__中mappings = dict()for k, v in attrs.iteritems():if isinstance(v, Field):#如果是Field类print('Found mapping: %s==>%s' % (k, v))mappings[k] = v#映射到mapping里for k in mappings.iterkeys():attrs.pop(k)attrs['__table__'] = name # 假设表名和类名一致attrs['__mappings__'] = mappings # 保存属性和列的映射关系return type.__new__(cls, name, bases, attrs)class Model(dict):__metaclass__ = ModelMetaclassdef __init__(self, **kw):super(Model, self).__init__(**kw)def __getattr__(self, key):try:return self[key]except KeyError:raise AttributeError(r"'Model' object has no attribute '%s'" % key)def __setattr__(self, key, value):self[key] = valuedef save(self):fields = []params = []args = []for k, v in self.__mappings__.iteritems():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):# 定义类的属性到列的映射：id = IntegerField('id')name = StringField('username')email = StringField('email')password = StringField('password')# 创建一个实例：
u = User(id='12345', name='Michael', email='test@orm.org', password='my-pwd')
# # 保存到数据库：
u.save()