用Metaclass实现一个精简的ORM框架-白红宇

存档：

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()

结果如下：

Found model: User

Found mapping: id ==> <IntegerField:id>

Found mapping: name ==> <StringField:username>

Found mapping: email ==> <StringField:email>

Found mapping: password ==> <StringField:password>

SQL: insert into User (id,username,email,password) values (?,?,?,?)

ARGS: [12345, 'Michael', 'test@orm.org', 'my-pwd']

[Finished in 0.2s]

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