This works. Thank you for the quick response and great libraries (I use
Mako as well).
Eric
On Fri, Aug 14, 2015 at 9:07 AM, Mike Bayer <mike...@zzzcomputing.com>
wrote:
> this code is incorrect from a Python perspective. You're removing the
> original `__init__` method entirely and it is never called; the attempt to
> call it using super() just calls object.__init__. SQLAlchemy is already
> decorating the __init__ method of the mapped class so you can't just throw
> it away, you can decorate it but you need to make sure its still called.
>
> Here is a plain demonstration without any SQLAlchemy:
>
> def licensed():
> def decorate(cls):
> def ___init__(self, **kwargs):
> print "magic new init!"
> super(cls, self).__init__(**kwargs)
> cls.__init__ = ___init__
> return cls
> return decorate
>
>
> @licensed()
> class SomeClass(object):
> def __init__(self):
> print "normal init!"
>
>
> SomeClass()
>
> Only "magic new init!" is printed. SomeClass.__init__ is never called.
>
>
> Here's the correct way to decorate a function in this context:
>
> def licensed(licenses):
> def decorate(cls):
> orig_init = cls.__init__
>
> def ___init__(self, **kwargs):
> for k, v in self.licenses.items():
> kwargs.setdefault('{}_license_rate'.format(k), v)
> orig_init(self, **kwargs)
> cls.__init__ = ___init__
>
>
>
>
>
>
> On 8/14/15 2:41 AM, Eric Atkin wrote:
>
> 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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