Hi,
I've written a class decorator to define a boilerplate __init__ on some of
my models that inherit from a declarative_base superclass. The problem is
that sqlalchemy.orm.instrumentation._generate_init() has already installed
an __init__ and when I overwrite that, things break with "object has no
attribute '_sa_instance_state'" exceptions. I've provided a sample below.
It actually throws a different exception than my code but I think the root
issue is the same, that is, my __init__ replaced the generated one and so
the ClassManager events are not being emitted.
Is there some blessed way to add an __init__ method after a class is
already defined or is that just impossible with sqlalchemy's
metaprogramming environment?
Love the library. Very powerful and excellent documentation. Thanks.
Eric
$ python
Python 2.7.10 (default, May 26 2015, 04:16:29)
[GCC 5.1.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import psycopg2
>>> import sqlalchemy
>>>
>>> psycopg2.__version__
'2.6 (dt dec pq3 ext lo64)'
>>> conn = psycopg2.connect("dbname=dispatch_dev")
>>> cur = conn.cursor()
>>> cur.execute("SELECT version();")
>>> cur.fetchone()
('PostgreSQL 9.4.4 on x86_64-unknown-linux-gnu, compiled by gcc (GCC)
5.1.0, 64-bit',)
>>>
>>> sqlalchemy.__version__
'0.9.7'
>>>
>>> from collections import OrderedDict
>>> from decimal import Decimal
>>> from sqlalchemy import Column, Integer, Numeric
>>> from sqlalchemy.ext.declarative import declarative_base
>>>
>>> def licensed(licenses):
... def decorate(cls):
... def ___init__(self, **kwargs):
... for k, v in self.licenses.items():
... kwargs.setdefault('{}_license_rate'.format(k), v)
... super(cls, self).__init__(**kwargs)
... cls.__init__ = ___init__
... for k, v in licenses.items():
... licenses[k] = Decimal(v)
... cls.licenses = licenses
... for license in licenses:
... setattr(cls, '{}_license_rate'.format(license), Column(
Numeric, nullable=False))
... return cls
... return decorate
...
>>>
>>> Base = declarative_base()
>>>
>>> @licensed(OrderedDict((('foo', 100), ('bar', 150))))
... class Instance_Link(Base):
... __tablename__ = 'instance_link'
... id = Column(Integer, primary_key=True)
...
>>> Instance_Link(foo_license_rate=50)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 6, in ___init__
File
"(...)/env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 526, in _declarative_constructor
setattr(self, k, kwargs[k])
File "(...)/env/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py",
line 225, in __set__
self.impl.set(instance_state(instance),
AttributeError: 'NoneType' object has no attribute 'set'
>>>
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