元類實現ORM
ORM 是 python編程語言後端web框架 Django的核心思想,“Object Relational Mapping”,即對象-關係映射,簡稱ORM。
一個句話理解就是:創建一個實例對象,用創建它的類名當做數據表名,用創建它的類屬性對應數據表的字段,當對這個實例對象操作時,能夠對應MySQL語句。
實例:
class ModelMetaclass(type):
def __new__(cls, name, bases, attrs):
mappings = dict()
# 判斷是否需要保存
for k, v in attrs.items():
# 判斷是否是指定的StringField或者IntegerField的實例對象
if isinstance(v, tuple):
print('Found mapping: %s ==> %s' % (k, v))
mappings[k] = v
# 刪除這些已經在字典中存儲的屬性
for k in mappings.keys():
attrs.pop(k)
# 將之前的uid/name/email/password以及對應的對象引用、類名字
attrs['__mappings__'] = mappings # 保存屬性和列的映射關係
attrs['__table__'] = name # 假設表名和類名一致
return type.__new__(cls, name, bases, attrs)
class Model(object, metaclass=ModelMetaclass):
def __init__(self, **kwargs):
for name, value in kwargs.items():
setattr(self, name, value)
def save(self):
fields = []
args = []
for k, v in self.__mappings__.items():
fields.append(v[0])
args.append(getattr(self, k, None))
args_temp = list()
for temp in args:
# 判斷入如果是數字類型
if isinstance(temp, int):
args_temp.append(str(temp))
elif isinstance(temp, str):
args_temp.append("""'%s'""" % temp)
sql = 'insert into %s (%s) values (%s)' % (self.__table__, ','.join(fields), ','.join(args_temp))
print('SQL: %s' % sql)
class User(Model):
uid = ('uid', "int unsigned")
name = ('username', "varchar(30)")
email = ('email', "varchar(30)")
password = ('password', "varchar(30)")
u = User(uid=12345, name='Michael', email='[email protected]', password='my-pwd')
# print(u.__dict__)
u.save()
作者:阿超
原創公衆號:『Python日常筆記』,專注於 Python爬蟲等技術棧和有益的程序人生,會將一些平時的日常筆記都慢慢整理起來,也期待你的關注和阿超一起學習,公衆號回覆【1024】優質資源。