ORM实现 

 1 #! /usr/bin/env python3
 2 #-*- coding:utf-8 -*-
 3 
 4 
 5 class Field(object):     
 6     def __init__(self, name, column_type):
 7         self.name = name
 8         self.column_type = column_type
 9 
10     def __str__(self):
11         return '<%s:%s>' % (self.__class__.__name__,self.name)
12 
13 class StringField(Field):
14     
15     def __init__(self, name):
16         super(StringField, self).__init__(name,'varchar(100)')
17 
18 class IntegerField(Field):
19     
20     def __init__(self, name):
21         super(IntegerField, self).__init__(name,'bigint')
22 
23 class ModelMetaclass(type):
24     
25     def __new__(cls,name,bases,attrs):
26         if name=='Model':
27             return type.__new__(cls,name,bases,attrs)
28 
29         print('Found model:%s'%name)
30         mappings = dict()
31         # 将属性放入mappings中
32         for k,v in attrs.items():
33             # 判断属性类型
34             if isinstance(v,Field):
35                 print('Found mapping:%s==>%s'%(k,v))
36                 mappings[k]=v
37         # 移除原有的属性
38         for k in mappings.keys():
39             attrs.pop(k)
40         # 新建__mappings__并将mappings赋值给它。将类名赋值给__table__
41         attrs['__mappings__']=mappings
42         attrs['__table__']= name
43         return type.__new__(cls,name,bases,attrs)
44 
45 class Model(dict,metaclass=ModelMetaclass):
46     
47     def __init__(self, **kw):
48         super(Model, self).__init__(**kw)
49     
50     def __getattr__(self,key):
51         try:
52             return self[key]
53         except KeyError:
54             raise AttributeError(r"'Model' object has no attribute '%s'"%key)
55     
56     def __setattr__(self,key,value):
57         self[key]= value
58     
59     def save(self):
60         fields = []
61         params = []
62         args = []
63         # 将__mappings__转换为SQL语句。并将数值放入Args中
64         for k,v in self.__mappings__.items():
65             fields.append(v.name)
66             params.append('?')
67             args.append(getattr(self,k,None))
68         sql = 'insert into %s(%s) values(%s)'%(self.__table__,','.join(fields),','.join(params))
69         print('SQL:%s'%sql)
70         print('ARGS:%s'%str(args))
71 
72 class User(Model):
73     # 定义类的属性到列的映射：
74     id = IntegerField('id')
75     name = StringField('username')
76     email = StringField('email')
77     password = StringField('password')
78 
79 # 创建一个实例：
80 u = User(id=12345, name='Michael', email='test@orm.org', password='my-pwd')
81 # 保存到数据库：
82 u.save()

 

  • 使用了类集成
  • 使用了元类（本质是一个类的模版，在新建时对类的属性进行处理）

输出结果

1 Found model:User
2 Found mapping:email==><StringField:email>
3 Found mapping:name==><StringField:username>
4 Found mapping:password==><StringField:password>
5 Found mapping:id==><IntegerField:id>
6 SQL:insert into User(password,username,email,id) values(?,?,?,?)
7 ARGS:['my-pwd', 'Michael', 'test@orm.org', 12345]

 

posted @ 2017-08-29 15:02  绝望的老猫  阅读(131)  评论(0)    收藏  举报