這篇文章將的很好, 推薦一下詳解orm
#!usr/bin/python
# -*- coding:utf8 -*-
# 實現ORM
# 定義Field類, 它負責保存數據庫表的字段名和字段類型
class Field(object):
def __init__(self, name, column_type):
self.name = name
self.column_type = column_type
def __str__(self):
# 對象的父類名:字段名
return '<%s:%s>' % (self.__class__.__name__, self.name)
# 在Field基礎上, 定義各種類型 如StringField, IntegerField等
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')
# 定義一個元類
class ModelMetaclass(type):
"""
cls: 動態修改的類
name: 動態修改的類名
bases: 代表被動態修改的類的所有父類
attr: 代表被動態修改的類的所有屬性、方法組成的字典
"""
def __new__(cls, name, bases, attrs):
print("-"*20, name, bases, 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)
# 保存屬性和列的映射關係
attrs['__mappings__'] = mappings
# 假設表名和類名一致
# attrs['__table__'] = name
attrs['__table__'] = attrs.get('Meta').table
return type.__new__(cls, name, bases, attrs)
class Model(dict, metaclass=ModelMetaclass):
def __init__(self, **kw):
print('**kw', kw)
super(Model, self).__init__(**kw)
# 調用對象.key的時候觸發
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))
class User(Model):
# 定義類的屬性到列的映射
id = IntegerField('id')
name = StringField('username')
email = StringField('email')
password = StringField('password')
class Meta:
table = "user"
# 創建一個實例
user = User(id=1, name='Clarence', email='[email protected]', password='123')
# 保存到數據庫
user.save()