Hi all,
Are there any best practices/caveats for overloading attribute access with
declarative sqlalchemy? I feel like the checks in setattr and getattr are
very hacky and are occasionally giving me strange surprises...
from sqlalchemy import Integer, String, Column, create_engine, PickleType
from sqlalchemy.orm import Session
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Foo(Base):
__tablename__ = 'foo'
id = Column(Integer, primary_key=True)
_instance_dict = Column(PickleType(mutable=True))
name = Column(String)
def __init__(self, name):
self._instance_dict = {}
self.name = name
def __setattr__(self, key, value):
if (key in self.__dict__ or key in self.__class__.__dict__ or
not hasattr(self, '_sa_instance_state') or
'AssociationProxy' in key):
# handle class-level attrs (like Columns) using default behavior
print 'setattr normal', key, value
Base.__setattr__(self, key, value)
else:
# regular python objects attached to as an attribute go to
pickled instance dict
print 'setattr other', key, value
self._instance_dict[key] = value
def __getattr__(self, key):
# use default behavior for looking up the dicts themselves
if key == '_instance_dict' and key not in self.__dict__:
self._sa_instance_state.initialize(key)
return getattr(self, key)
# check for the key in regular python object dict and sqlobjects
dict
try:
return self._instance_dict[key]
except KeyError:
return Base.__getattr__(self, key)
engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)
session = Session(engine)
# create a new animal
a = Foo('aardvark')
a.test = 10
session.add(a)
session.commit()
session.close()
for foo in session.query(Foo):
print foo, foo.name, foo.test
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