Python中编写ORM框架的入门指引

user = User.get('123')

u = db.select_one('select * from users where id=?', '123')
user = User(**u)

from transwarp.orm import Model, StringField, IntegerField
 
class User(Model):
__table__ = 'users'
id = IntegerField(primary_key=True)
name = StringField()

# 创建实例:
user = User(id=123, name='Michael')
# 存入数据库:
user.insert()

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"'Dict' object has no attribute '%s'" % key)
 
def __setattr__(self, key, value):
self[key] = value

>>> user['id']
123
>>> user.id
123

class ModelMetaclass(type):
def __new__(cls, name, bases, attrs):
mapping = ... # 读取cls的Field字段
primary_key = ... # 查找primary_key字段
__table__ = cls.__talbe__ # 读取cls的__table__字段
# 给cls增加一些字段：
attrs['__mapping__'] = mapping
attrs['__primary_key__'] = __primary_key__
attrs['__table__'] = __table__
return type.__new__(cls, name, bases, attrs)

class Model(dict):
 
...
 
@classmethod
def get(cls, pk):
d = db.select_one('select * from %s where %s=?' % (cls.__table__, cls.__primary_key__.name), pk)
return cls(**d) if d else None

class Model(dict):
 
...
 
def insert(self):
params = {}
for k, v in self.__mappings__.iteritems():
params[v.name] = getattr(self, k)
db.insert(self.__table__, **params)
return self

user = User(id=123, name='Michael')
user.insert()

find_first()
 
find_all()
 
find_by()

count_all()
 
count_by()