1，使用type()函数运行时动态创建Class
2，定义metaclass类从type类继承，重写__new__方法，注意区分Model类和从Model继承的子类
3，定义模板类Model，使用__metaclass__ = metaclass元类
4，定义User类从Model类继承实现“Object Relational Mapping”，即对象-关系映射
#!/usr/bin/python
#-*- coding: utf-8 -*-
class Field(object):
"""docstring for Field"""
def __init__(self, name, colum_type):
super(Field, self).__init__()
self.name = name
self.colum_type = colum_type
def __str__(self):
return '<%s:%s>' %(self.__class__.__name__, self.name)
class StringField(Field):
"""docstring for StringField"""
def __init__(self, name):
super(StringField, self).__init__(name, 'varchar(100)')
class IntegerField(Field):
"""docstring for IntegerField"""
def __init__(self, name):
super(IntegerField, self).__init__(name, 'bigint')
class ModelMetaclass(type):
"""docstring for ModelMetaclass"""
def __new__(cls, name, bases, attrs):
print 'ModelMetaclass', cls, name, bases, attrs
if name == 'Model': #区分Model与其子类型
return type.__new__(cls, name, bases, attrs)
print 'Found model:%s' %name
mappings = dict()
for k, v in attrs.iteritems():
if isinstance(v, Field):
print 'Found mappings: %s ==> %s' %(k, v)
mappings[k] = v
#删除Model子类的同名属性
for k in mappings.iterkeys():
attrs.pop(k)
attrs['__mappings__'] = mappings
attrs['__table__'] = name
return type.__new__(cls, name, bases, attrs)
class Model(dict):
"""docstring for Model"""
__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' %key)
def __setattr__(self, key, value):
self[key] = value
def save(self):
field = []
params = []
args = []
for k, v in self.__mappings__.iteritems():
field.append(v.name)
params.append('?')
args.append(getattr(self, k, None))
sql = 'insert into %s (%s) values (%s)' %(self.__table__, ','.join(field), ','.join(params))
print 'Sql: %s' %sql
print 'ARGS: %s' %str(args)
class User(Model):
"""docstring for User"""
def __init__(self, **kw):
super(User, self).__init__(**kw)
id = IntegerField('uid')
name = StringField('username')
email = StringField('email')
password = StringField('password')
def main():
#“Object Relational Mapping”，即对象-关系映射
u = User(id='123456', name='Mick', email='mick@gmail.com', password='12345678')
u.save()
if __name__ == '__main__':
main()
