概要
本文仅仅是对廖雪峰老师的使用元类自定义ORM进行改进，并不是要创建一个ORM框架
编写field
class Field(object):def __init__(self, column_type,max_length,**kwargs):'''1，删除了参数name，field参数全部为定义字段类型相关参数，和众多有名的orm相同2，使用反射，方便字段的扩展，如本例使用deafault就是反射的应用'''self.column_type = column_type #字段类型self.max_length=max_length #字段长度self.default=None #字段默认值，如果想扩展可以填写更多的参数if kwargs:for k,v in kwargs.items():if hasattr(self,k):setattr(self,k,v)def __str__(self):return '<%s>' % (self.__class__.__name__)class StringField(Field):def __init__(self,max_length,**kwargs):super().__init__(column_type='varchar({})'.format(max_length),max_length=max_length,**kwargs)class IntegerField(Field):def __init__(self,**kwargs):super().__init__(column_type='bigint',max_length=8)编写metaclass
class ModelMetaclass(type):def __new__(cls, name, bases, attrs):if name=='Model':return type.__new__(cls, name, bases, attrs)mappings = dict()for k, v in attrs.items():#print('k={},v={}'.format(k,v))if isinstance(v, Field):mappings[k] = vfor k in mappings.keys():attrs.pop(k)attrs['__mappings__'] = mappings # 保存属性和列的映射关系attrs['__table__'] = attrs.get('Meta').table or name # 假设表名和类名一致return type.__new__(cls, name, bases, attrs)编写model
class Model(dict, metaclass=ModelMetaclass):def __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 = []for k, v in self.__mappings__.items():fields.append(k)params.append(getattr(self, k,v.default))sql = 'insert into {} ({}) values ({})'.format(self.__table__, self.join(fields) ,self.join(params))print('SQL: %s' % sql)#自己写了一个join函数，廖雪峰老师使用自带join，无法处理数字等非字符串类型import functoolsdef join(self,attrs,pattern=','):return functools.reduce(lambda x,y:'{}{}{}'.format(x,pattern,y),attrs)测试
class User(Model):#使用Meta，能自定义表的相关信息class Meta:#自定义表名table='users'# 定义类的属性到列的映射：id = IntegerField()name = StringField(max_length=50)email = StringField(max_length=50,default='root@123.com')password = StringField(max_length=50)if __name__=="__main__":# 创建一个实例：u=User(id=234,name='jane',password='pwd')# 保存到数据库：u.save()#打印结果;SQL: insert into users (id,name,email,password) values (234,jane,root@123.com,pwd)引用
1, 廖雪峰：使用元类
2, github：本文源码
