寫一個簡單的ORM
摘要：
最近在研究SQLAlchemy原始碼，自己造個輪子先（當然，SQLAlchemy遠比這裡複雜）
import logging
logging.basicConfig(level=logging.DEBUG)
class Column:
def __init__(self, t...
最近在研究SQLAlchemy原始碼，自己造個輪子先（當然，SQLAlchemy遠比這裡複雜）
import logging
logging.basicConfig(level=logging.DEBUG)
class Column:
def __init__(self, type, default=None):
self.col_name = None
self.col_type = type
self.col_default = default
def __eq__(self, value):
logging.debug("__eq__ of {} && {}".format(self, value))
return "{} = {}".format(self.col_name, value)
class Base(type):
def __new__(cls, *args, **kwargs):
logging.debug("creating class {}, args {}, kwargs {}".format(
cls, args, kwargs
))
if len(args) > 2:
for k, v in args[2].items():
if k.startswith("_"):
continue
v.col_name = k
return type.__new__(cls, *args, **kwargs)
class User(metaclass=Base):
__tablename__ = "user"
id = Column(int)
name = Column(str)
passwd = Column(str)
class Queryable:
def __init__(self, table):
self.table = table
def filter(self, text):
return "select * from {} where {}".format(
self.table.__tablename__,
text,
)
class Session:
def query(self, table):
logging.debug("returning Queryable({})".format(table))
return Queryable(table)
session = Session()
print(session.query(User).filter(User.id == 1))
執行結果：
jiajun@debian test: python3 orm.py
DEBUG:root:creating class <class '__main__.Base'>, args ('User', (), {'__qualname__': 'User', '__tablename__': 'user', 'id': <__main__.Column object at 0x7f8174b107b8>, 'passwd': <__main__.Column object at 0x7f8174b10940>, 'name': <__main__.Column object at 0x7f8174b10828>, '__module__': '__main__'}), kwargs {}
DEBUG:root:returning Queryable(<class '__main__.User'>)
DEBUG:root:__eq__ of <__main__.Column object at 0x7f8174b107b8> && 1
select * from user where id = 1