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83 lines (68 loc) · 2.69 KB
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#!/usr/bin/env python
# -*- coding: utf-8 -*-
class Field(object):
def __init__(self, name, column_type):
self.name = name
self.column_type = column_type
def __str__(self):
return '<%s:%s>' % (self.__class__.__name__, self.name)
class StringField(Field):
def __init__(self, name):
super(StringField, self).__init__(name, 'varchar(100)')
class IntegerField(Field):
def __init__(self, name):
super(IntegerField, self).__init__(name, 'bigint')
class ModelMetaclass(type):
def __new__(cls, name, bases, attrs):
print(cls)
print(name)
print(bases)
print(attrs)
if name=='Model':
return type.__new__(cls, name, bases, attrs)
print('Found model: %s' % name)
mappings = dict()
for k, v in attrs.items():
if isinstance(v, Field):
print('Found mapping: %s ==> %s' % (k, v))
mappings[k] = v
for k in mappings.keys():
attrs.pop(k)
attrs['__mappings__'] = mappings # 保存属性和列的映射关系
attrs['__table__'] = name # 假设表名和类名一致
return type.__new__(cls, name, bases, attrs)
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] = value
def save(self):
fields = []
params = []
args = []
for k, v in self.__mappings__.items():
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))
# testing code:
#当用户写下class User(Model)时，类对象User还没有在内存中创建，Python解释器首先在当前类User的定义中查找metaclass，如果没有找到，
#就继续在父类Model中查找metaclass，找到了，就使用Model中定义的metaclass的ModelMetaclass来创建User类，
#也就是说，metaclass可以隐式地继承到子类，但子类自己却感觉不到。
class User(Model):
id = IntegerField('id')
name = StringField('username')
email = StringField('email')
password = StringField('password')
def __init__(self, **kw):
super(User, self).__init__(**kw)
#instance(u, dict)=True,u是一个字典
u.save()