[sqlalchemy] Overwriting __init__() after class definition breaks sqlalchemy with declarative
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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Re: [sqlalchemy] Overwriting __init__() after class definition breaks sqlalchemy with declarative
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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Re: [sqlalchemy] override relationship in subclass
Yeah sorry I missed that. conversion is an attribute on Measured_Source.
So the intent is that a Production_Load is a Load with its own additional
attributes over Load as well as a constraint that its source is a
Measured_Source which has its own attribute extensions over Source. One of
the goals here is to add that constraint enforcement. I was able to make it
work with the following hybrid_method and hybrid_method.expression, but the
isinstance(Production_Load.source, Measured_Source) enforcement is missing.
Eric
{{{
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
top = Column(Numeric, nullable=False)
bottom = Column(Numeric, nullable=False)
@hybrid_method
def delta(self):
return (self.top-self.bottom)*self.source.conversion if self.source
else None
@gdelta.expression
def delta(self):
# not sure about the performance here
return
(self.top-self.bottom)*select([Measured_Source.conversion]).where(Measured_Source.id==self.source_id).label('delta')
}}}
On Wednesday, February 12, 2014 7:17:08 AM UTC-7, Michael Bayer wrote:
On Feb 11, 2014, at 9:38 PM, Eric Atkin eat...@certusllc.us javascript:
wrote:
Hi,
I want to override a relationship in a subclass to relate to a subclass
of the base attributes' related class. Perhaps an example of how I thought
it should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source - Source and I want
Production_Load.source - Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship
on inherited mapper 'Mapper|Load|load'; this can cause dependency issues
during flush
and when I try to use Production_Load.source (class level attr) in a
query, I get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
“conversion” sounds like an attribute name on your end, but generally
being able to supersede a relationship like that when the inheritance is
not “concrete” is not supported. you’d need to name it to something else.
--
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Re: [sqlalchemy] override relationship in subclass
@gdelta.expression is a typo. Should be @delta.expression.
On Wednesday, February 12, 2014 11:53:05 AM UTC-7, Eric Atkin wrote:
Yeah sorry I missed that. conversion is an attribute on Measured_Source.
So the intent is that a Production_Load is a Load with its own additional
attributes over Load as well as a constraint that its source is a
Measured_Source which has its own attribute extensions over Source. One of
the goals here is to add that constraint enforcement. I was able to make it
work with the following hybrid_method and hybrid_method.expression, but the
isinstance(Production_Load.source, Measured_Source) enforcement is missing.
Eric
{{{
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
top = Column(Numeric, nullable=False)
bottom = Column(Numeric, nullable=False)
@hybrid_method
def delta(self):
return (self.top-self.bottom)*self.source.conversion if
self.source else None
@gdelta.expression
def delta(self):
# not sure about the performance here
return
(self.top-self.bottom)*select([Measured_Source.conversion]).where(Measured_Source.id==self.source_id).label('delta')
}}}
On Wednesday, February 12, 2014 7:17:08 AM UTC-7, Michael Bayer wrote:
On Feb 11, 2014, at 9:38 PM, Eric Atkin eat...@certusllc.us wrote:
Hi,
I want to override a relationship in a subclass to relate to a subclass
of the base attributes' related class. Perhaps an example of how I thought
it should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source - Source and I want
Production_Load.source - Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship
on inherited mapper 'Mapper|Load|load'; this can cause dependency issues
during flush
and when I try to use Production_Load.source (class level attr) in a
query, I get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
“conversion” sounds like an attribute name on your end, but generally
being able to supersede a relationship like that when the inheritance is
not “concrete” is not supported. you’d need to name it to something else.
--
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[sqlalchemy] override relationship in subclass
Hi,
I want to override a relationship in a subclass to relate to a subclass of
the base attributes' related class. Perhaps an example of how I thought it
should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source - Source and I want
Production_Load.source - Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship
on inherited mapper 'Mapper|Load|load'; this can cause dependency issues
during flush
and when I try to use Production_Load.source (class level attr) in a query,
I get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
Thanks,
Eric
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