Re: [sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
the first error is because declarative isn't smart enough to figure out
this many __abstract__ flags, and I'd support efforts to improve this.
But if you pass __abstract__ = False in a few places that gives it the
clues it needs to get to the second case (as well as removing the
__abstract__ = True where not needed).
The second error is more simple, you need to define what table Coupe is
mapped towards; if you want it to be single inheritance off of "cars"
then you need to give it None for __tablename__:
class Vehicle(AbstractVehicle, Base):
pass
class Car(AbstractCar, Vehicle):
__abstract__ = False
class Coupe(AbstractCoupe, Car):
__abstract__ = False
__tablename__ = None
BEGIN (implicit)
2016-07-22 09:35:58,641 INFO sqlalchemy.engine.base.Engine INSERT INTO
vehicles (id, name, type) VALUES (?, ?, ?)
2016-07-22 09:35:58,641 INFO sqlalchemy.engine.base.Engine (10, 'test',
'coupe')
2016-07-22 09:35:58,642 INFO sqlalchemy.engine.base.Engine INSERT INTO
cars (id) VALUES (?)
2016-07-22 09:35:58,642 INFO sqlalchemy.engine.base.Engine (10,)
2016-07-22 09:35:58,642 INFO sqlalchemy.engine.base.Engine COMMIT
2016-07-22 09:35:58,643 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-07-22 09:35:58,644 INFO sqlalchemy.engine.base.Engine SELECT
cars.id AS cars_id, vehicles.id AS vehicles_id, vehicles.name AS
vehicles_name, vehicles.type AS vehicles_type
FROM vehicles JOIN cars ON vehicles.id = cars.id
WHERE vehicles.type IN (?)
LIMIT ? OFFSET ?
2016-07-22 09:35:58,644 INFO sqlalchemy.engine.base.Engine ('coupe', 1, 0)
<__main__.Coupe object at 0x7f4a81e5afd0>
On 07/21/2016 07:22 PM, Angie Ellis wrote:
Adding __abstract__ = True to the AbstractCoupe did seem to resolve
those errors, but it gave me a new one:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr
class AbstractVehicle(object):
__tablename__ = "vehicles"
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
type = Column(String)
__mapper_args__ = {"polymorphic_on": type}
class AbstractCar(AbstractVehicle):
__tablename__ = "cars"
id = Column("id", Integer, primary_key=True)
__mapper_args__ = {"polymorphic_identity": "car"}
__table_args__ = (
ForeignKeyConstraint(["id"], ["vehicles.id "]),
)
class AbstractCoupe(AbstractCar):
__abstract__ = True
__mapper_args__ = {"polymorphic_identity": "coupe"}
Base = declarative_base()
class Vehicle(AbstractVehicle, Base):
pass
class Car(AbstractCar, Vehicle):
pass
class Coupe(AbstractCoupe, Car):
pass
if __name__ == "__main__":
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
s.add(Coupe(id=10, name="test"))
s.commit()
s.close()
b1 = s.query(Coupe).first()
print(b1)
Traceback (most recent call last):
File "test.py", line 53, in
s.add(Coupe(id=10, name="test"))
File "", line 4, in __init__
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/state.py",
line 306, in _initialize_instance
manager.dispatch.init_failure(self, args, kwargs)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py",
line 60, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
line 184, in reraise
raise value
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/state.py",
line 303, in _initialize_instance
return manager.original_init(*mixed[1:], **kwargs)
File "", line 6, in __init__
File "", line 6, in __init__
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/ext/declarative/base.py",
line 649, in _declarative_constructor
setattr(self, k, kwargs[k])
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/attributes.py",
line 223, in __set__
self.impl.set(instance_state(instance),
AttributeError: 'NoneType' object has no attribute 'set'
When I take out the arguments and just run:
s.add(Coupe())
It gives me this:
Traceback (most recent call last):
File "test.py", line 53, in
s.add(Coupe())
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
line 1588, in add
self._save_or_update_state(state)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
line 1602, in _save_or_update_state
mapper = _state_mapper(state)
File
Re: [sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
Adding __abstract__ = True to the AbstractCoupe did seem to resolve those
errors, but it gave me a new one:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr
class AbstractVehicle(object):
__tablename__ = "vehicles"
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
type = Column(String)
__mapper_args__ = {"polymorphic_on": type}
class AbstractCar(AbstractVehicle):
__tablename__ = "cars"
id = Column("id", Integer, primary_key=True)
__mapper_args__ = {"polymorphic_identity": "car"}
__table_args__ = (
ForeignKeyConstraint(["id"], ["vehicles.id"]),
)
class AbstractCoupe(AbstractCar):
__abstract__ = True
__mapper_args__ = {"polymorphic_identity": "coupe"}
Base = declarative_base()
class Vehicle(AbstractVehicle, Base):
pass
class Car(AbstractCar, Vehicle):
pass
class Coupe(AbstractCoupe, Car):
pass
if __name__ == "__main__":
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
s.add(Coupe(id=10, name="test"))
s.commit()
s.close()
b1 = s.query(Coupe).first()
print(b1)
Traceback (most recent call last):
File "test.py", line 53, in
s.add(Coupe(id=10, name="test"))
File "", line 4, in __init__
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/state.py",
line 306, in _initialize_instance
manager.dispatch.init_failure(self, args, kwargs)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py",
line 60, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
line 184, in reraise
raise value
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/state.py",
line 303, in _initialize_instance
return manager.original_init(*mixed[1:], **kwargs)
File "", line 6, in __init__
File "", line 6, in __init__
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/ext/declarative/base.py",
line 649, in _declarative_constructor
setattr(self, k, kwargs[k])
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/attributes.py",
line 223, in __set__
self.impl.set(instance_state(instance),
AttributeError: 'NoneType' object has no attribute 'set'
When I take out the arguments and just run:
s.add(Coupe())
It gives me this:
Traceback (most recent call last):
File "test.py", line 53, in
s.add(Coupe())
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
line 1588, in add
self._save_or_update_state(state)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
line 1602, in _save_or_update_state
mapper = _state_mapper(state)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py",
line 754, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File
"/mnt/hgfs/Documents/git/cc-mysql/env/lib/python3.5/site-packages/sqlalchemy/orm/instrumentation.py",
line 116, in mapper
raise exc.UnmappedClassError(self.class_)
sqlalchemy.orm.exc.UnmappedClassError: Class '__main__.Coupe' is not mapped
Sorry for the intermittent responses. Thanks so much for your help!
On Mon, Jun 27, 2016 at 2:21 PM, Mike Bayer
wrote:
> I think it's OK to add __abstract__ to those mixins, in this case it seems
> like the (pretty complicated) class graph is adding up to something that
> causes declarative to see AbstractCar as mapped class thus a "car" table is
> added. Adding __abstract__ to AbstractCoupe seems to resolve.
>
>
>
>
> On 06/27/2016 05:10 PM, Angie Ellis wrote:
>
>> I implemented the changes you suggested, but I am running into errors
>> with some polymorphic relations. Using a different theme, here is an
>> example:
>>
>>
>> class AbstractVehicle(object):
>> __tablename__ = "vehicles"
>>
>> id = Column(Integer, primary_key=True)
>> name = Column(String, nullable=False)
>> type = Column(String)
>>
>> __mapper_args__ = {"polymorphic_on": type}
>>
>>
>> class AbstractCar(AbstractVehicle):
>> __tablename__ = "cars"
>>
>> id = Column("id", Integer, primary_key=True)
>>
>> __mapper_args__ = {"polymorphic_identity": "car"}
>> __table_args__ = (
>> ForeignKeyConstraint(["id"], ["vehicles.id > >"]),
>>
>> )
Re: [sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
I think it's OK to add __abstract__ to those mixins, in this case it
seems like the (pretty complicated) class graph is adding up to
something that causes declarative to see AbstractCar as mapped class
thus a "car" table is added. Adding __abstract__ to AbstractCoupe seems
to resolve.
On 06/27/2016 05:10 PM, Angie Ellis wrote:
I implemented the changes you suggested, but I am running into errors
with some polymorphic relations. Using a different theme, here is an
example:
class AbstractVehicle(object):
__tablename__ = "vehicles"
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
type = Column(String)
__mapper_args__ = {"polymorphic_on": type}
class AbstractCar(AbstractVehicle):
__tablename__ = "cars"
id = Column("id", Integer, primary_key=True)
__mapper_args__ = {"polymorphic_identity": "car"}
__table_args__ = (
ForeignKeyConstraint(["id"], ["vehicles.id "]),
)
class AbstractCoupe(AbstractCar):
__mapper_args__ = {"polymorphic_identity": "coupe"}
Base = declarative_base()
class Vehicle(AbstractVehicle, Base):
pass
class Car(AbstractCar, Vehicle):
pass
class Coupe(AbstractCoupe, Car):
pass
This resulted in the following error:
File ".../model/vehicle.py", line 255, in
class Coupe(AbstractCoupe, Car):
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py",
line 55, in __init__
_as_declarative(cls, classname, cls.__dict__)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
88, in _as_declarative
_MapperConfig.setup_mapping(cls, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
103, in setup_mapping
cfg_cls(cls_, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
131, in __init__
self._setup_table()
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
395, in _setup_table
**table_kw)
File ".../env/lib/python2.7/site-packages/sqlalchemy/sql/schema.py",
line 398, in __new__
"existing Table object." % key)
InvalidRequestError: Table 'cars' is already defined for this MetaData
instance. Specify 'extend_existing=True' to redefine options and
columns on an existing Table object.
After adding "extend_existing=True" to the AbstractCoupe model, I
received this error:
File ".../model/vehicle.py", line 255, in
class Coupe(AbstractCoupe, Car):
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py",
line 55, in __init__
_as_declarative(cls, classname, cls.__dict__)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
88, in _as_declarative
_MapperConfig.setup_mapping(cls, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
103, in setup_mapping
cfg_cls(cls_, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
135, in __init__
self._early_mapping()
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
138, in _early_mapping
self.map()
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line
530, in map
**self.mapper_args
File "", line 2, in mapper
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 627, in __init__
self._configure_properties()
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 1292, in _configure_properties
self._adapt_inherited_property(key, prop, False)
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 1514, in _adapt_inherited_property
self._configure_property(key, prop, init=False, setparent=False)
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py",
line 1541, in _configure_property
prop.columns[0])
File
".../env/lib/python2.7/site-packages/sqlalchemy/sql/selectable.py", line
476, in corresponding_column
if self.c.contains_column(column):
File
".../env/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
line 754, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File
".../env/lib/python2.7/site-packages/sqlalchemy/sql/selectable.py", line
553, in columns
return self._columns.as_immutable()
AttributeError: 'Table' object has no attribute '_columns'
Is there a way to fix or work around this?
Thanks,
Angie
On Wed, Jun 22, 2016 at 7:27 PM, Mike Bayer > wrote:
On 06/22/2016 04:53 PM, Angie Ellis wrote:
Mike,
Thank you for the response! I do have control over the external
library.
I like your idea having both the abstract classes and concrete
classes
available in the library because I have use cases for both in my
Re: [sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
I implemented the changes you suggested, but I am running into errors with
some polymorphic relations. Using a different theme, here is an example:
class AbstractVehicle(object):
__tablename__ = "vehicles"
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
type = Column(String)
__mapper_args__ = {"polymorphic_on": type}
class AbstractCar(AbstractVehicle):
__tablename__ = "cars"
id = Column("id", Integer, primary_key=True)
__mapper_args__ = {"polymorphic_identity": "car"}
__table_args__ = (
ForeignKeyConstraint(["id"], ["vehicles.id"]),
)
class AbstractCoupe(AbstractCar):
__mapper_args__ = {"polymorphic_identity": "coupe"}
Base = declarative_base()
class Vehicle(AbstractVehicle, Base):
pass
class Car(AbstractCar, Vehicle):
pass
class Coupe(AbstractCoupe, Car):
pass
This resulted in the following error:
File ".../model/vehicle.py", line 255, in
class Coupe(AbstractCoupe, Car):
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py",
line 55, in __init__
_as_declarative(cls, classname, cls.__dict__)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 88, in _as_declarative
_MapperConfig.setup_mapping(cls, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 103, in setup_mapping
cfg_cls(cls_, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 131, in __init__
self._setup_table()
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 395, in _setup_table
**table_kw)
File ".../env/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line
398, in __new__
"existing Table object." % key)
InvalidRequestError: Table 'cars' is already defined for this MetaData
instance. Specify 'extend_existing=True' to redefine options and columns
on an existing Table object.
After adding "extend_existing=True" to the AbstractCoupe model, I received
this error:
File ".../model/vehicle.py", line 255, in
class Coupe(AbstractCoupe, Car):
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py",
line 55, in __init__
_as_declarative(cls, classname, cls.__dict__)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 88, in _as_declarative
_MapperConfig.setup_mapping(cls, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 103, in setup_mapping
cfg_cls(cls_, classname, dict_)
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 135, in __init__
self._early_mapping()
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 138, in _early_mapping
self.map()
File
".../env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py",
line 530, in map
**self.mapper_args
File "", line 2, in mapper
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
627, in __init__
self._configure_properties()
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
1292, in _configure_properties
self._adapt_inherited_property(key, prop, False)
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
1514, in _adapt_inherited_property
self._configure_property(key, prop, init=False, setparent=False)
File ".../env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
1541, in _configure_property
prop.columns[0])
File ".../env/lib/python2.7/site-packages/sqlalchemy/sql/selectable.py",
line 476, in corresponding_column
if self.c.contains_column(column):
File
".../env/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line
754, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File ".../env/lib/python2.7/site-packages/sqlalchemy/sql/selectable.py",
line 553, in columns
return self._columns.as_immutable()
AttributeError: 'Table' object has no attribute '_columns'
Is there a way to fix or work around this?
Thanks,
Angie
On Wed, Jun 22, 2016 at 7:27 PM, Mike Bayer
wrote:
>
>
> On 06/22/2016 04:53 PM, Angie Ellis wrote:
>
>> Mike,
>>
>> Thank you for the response! I do have control over the external library.
>> I like your idea having both the abstract classes and concrete classes
>> available in the library because I have use cases for both in my
>> applications. However, I'm not quite sure how to configure the
>> inheritance and declarative base. What am I doing wrong here?
>>
>>
>> class AbstractFoo(object):
>> __abstract__ = True
>> __tablename__ = "foo"
>> id = Column(Integer, primary_key=True)
>> type = Column(String)
>> foo_bar_id = Column(Integer, ForeignKey("foo_bar.id
>> "))
>> foo_bar = relationship("FooBar",
Re: [sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
On 06/22/2016 04:53 PM, Angie Ellis wrote:
Mike,
Thank you for the response! I do have control over the external library.
I like your idea having both the abstract classes and concrete classes
available in the library because I have use cases for both in my
applications. However, I'm not quite sure how to configure the
inheritance and declarative base. What am I doing wrong here?
class AbstractFoo(object):
__abstract__ = True
__tablename__ = "foo"
id = Column(Integer, primary_key=True)
type = Column(String)
foo_bar_id = Column(Integer, ForeignKey("foo_bar.id
"))
foo_bar = relationship("FooBar", backref=backref("foo"))
__mapper_args__ = {"polymorphic_on": type}
class AbstractBar(object):
__abstract__ = True
__mapper_args__ = {"polymorphic_identity": "bar"}
class AbstractFooBar(object):
__abstract__ = True
__tablename__ = "foo_bar"
id = Column(Integer, primary_key=True)
Base = declarative_base()
class Foo(AbstractFoo, Base):
pass
class Bar(AbstractBar, Foo):
pass
class FooBar(AbstractFooBar, Base):
pass
Does AbstractBar need to inherit from AbstractFoo? Do the abstract
classes need to inherit their own declarative base? Do I need to change
the inheritance order? The classes Foo, Bar, and FooBar are not getting
mapped.
So the way you have it is that those are mixins, which is fine, and I
guess that's how we need it because you want to keep multiple Base's in
play at the same time. You don't need the __abstract__ keyword in that
case. So to map that looks like the following POC:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr
class AbstractFoo(object):
__tablename__ = "foo"
id = Column(Integer, primary_key=True)
type = Column(String)
@declared_attr
def foo_bar_id(cls):
return Column(Integer, ForeignKey("foo_bar.id"))
@declared_attr
def foo_bar(cls):
return relationship("FooBar", backref=backref("foo"))
__mapper_args__ = {"polymorphic_on": type}
class AbstractBar(AbstractFoo):
__mapper_args__ = {"polymorphic_identity": "bar"}
class AbstractFooBar(object):
__tablename__ = "foo_bar"
id = Column(Integer, primary_key=True)
Base = declarative_base()
class Foo(AbstractFoo, Base):
pass
class Bar(AbstractBar, Foo):
pass
class FooBar(AbstractFooBar, Base):
pass
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
s.add(Bar(foo_bar=FooBar()))
s.commit()
s.close()
b1 = s.query(Foo).first()
print b1
print b1.foo_bar
Thanks,
Angie
On Fri, Jun 3, 2016 at 12:38 PM, Mike Bayer > wrote:
On 06/03/2016 02:44 PM, Angie E wrote:
Rather than creating mixin classes that models inherit from, I
have a
use case that requires me to configure classes the other way
around. The
classes that would normally be mixin classes need to be the
classes that
inherit from the models as well as the class that model objects are
created from. This is because the models and the mapper
configurations
are in an external library from the main repository. I need to
pass in
the host for the engine from the main repository to the models
library
before any of the models are loaded so they can load with the
declarative base already configured.
I hope you are using reflection for these models, otherwise there's
no reason to have a depedency on the Engine for the model declaration.
After the engine information is
passed in, the session, Base class, and everything is created
within a
sort of base class that the models inherit from. Here is a
simplified
example:
class SQLAlchemyBase(object):
metadata = None
Session = None
Base = object
sessionfactory = sessionmaker()
def initialize(self, host):
engine = create_engine(host)
self.metadata = MetaData(bind=engine)
self.Session = scoped_session(self.sessionfactory)
self.Base = declarative_base(metadata=self.metadata)
models = SQLAlchemyBase()
(The models inherit from models.Base)
So the SQLAlchemyBase will be imported into the main repository, the
initialize method will be called, passing in the host for the
engine,
and the models can then be imported.
Looks like no reflection taking place. I'd do away with the
MetaData(bind=engine), and just have the engine as part of the
sessionmaker(), and the sessionmaker() here also doesn't need to
have anything to do with the "library", if the "library" is just
defining model
Re: [sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
Mike,
Thank you for the response! I do have control over the external library. I
like your idea having both the abstract classes and concrete classes
available in the library because I have use cases for both in my
applications. However, I'm not quite sure how to configure the inheritance
and declarative base. What am I doing wrong here?
class AbstractFoo(object):
__abstract__ = True
__tablename__ = "foo"
id = Column(Integer, primary_key=True)
type = Column(String)
foo_bar_id = Column(Integer, ForeignKey("foo_bar.id"))
foo_bar = relationship("FooBar", backref=backref("foo"))
__mapper_args__ = {"polymorphic_on": type}
class AbstractBar(object):
__abstract__ = True
__mapper_args__ = {"polymorphic_identity": "bar"}
class AbstractFooBar(object):
__abstract__ = True
__tablename__ = "foo_bar"
id = Column(Integer, primary_key=True)
Base = declarative_base()
class Foo(AbstractFoo, Base):
pass
class Bar(AbstractBar, Foo):
pass
class FooBar(AbstractFooBar, Base):
pass
Does AbstractBar need to inherit from AbstractFoo? Do the abstract classes
need to inherit their own declarative base? Do I need to change the
inheritance order? The classes Foo, Bar, and FooBar are not getting mapped.
Thanks,
Angie
On Fri, Jun 3, 2016 at 12:38 PM, Mike Bayer
wrote:
>
>
> On 06/03/2016 02:44 PM, Angie E wrote:
>
>> Rather than creating mixin classes that models inherit from, I have a
>> use case that requires me to configure classes the other way around. The
>> classes that would normally be mixin classes need to be the classes that
>> inherit from the models as well as the class that model objects are
>> created from. This is because the models and the mapper configurations
>> are in an external library from the main repository. I need to pass in
>> the host for the engine from the main repository to the models library
>> before any of the models are loaded so they can load with the
>> declarative base already configured.
>>
>
> I hope you are using reflection for these models, otherwise there's no
> reason to have a depedency on the Engine for the model declaration.
>
>
> After the engine information is
>
>> passed in, the session, Base class, and everything is created within a
>> sort of base class that the models inherit from. Here is a simplified
>> example:
>>
>>
>> class SQLAlchemyBase(object):
>> metadata = None
>> Session = None
>> Base = object
>> sessionfactory = sessionmaker()
>>
>> def initialize(self, host):
>> engine = create_engine(host)
>> self.metadata = MetaData(bind=engine)
>> self.Session = scoped_session(self.sessionfactory)
>> self.Base = declarative_base(metadata=self.metadata)
>>
>> models = SQLAlchemyBase()
>>
>> (The models inherit from models.Base)
>>
>>
>> So the SQLAlchemyBase will be imported into the main repository, the
>> initialize method will be called, passing in the host for the engine,
>> and the models can then be imported.
>>
>
> Looks like no reflection taking place. I'd do away with the
> MetaData(bind=engine), and just have the engine as part of the
> sessionmaker(), and the sessionmaker() here also doesn't need to have
> anything to do with the "library", if the "library" is just defining model
> classes.
>
> The "bound metadata" pattern is highly discouraged in modern SQLAlchemy
> because it leads to this kind of confusion, e.g. that one needs an Engine
> in order to declare models. You don't.
>
>
>
>
>
>
> The main repository has its own
>
>> classes with the same names as the models and have additional methods
>> that a normal mixin class would have to extend functionality. However, I
>> am unable to create model objects using the classes in the main
>> repository because I can't get the mappers to play nice with this
>> unusual inheritance that extends from the external models library.
>> Additionally, in the models library, there are models that have multiple
>> levels of inherited polymorphic relationships. Here is an example that
>> is similar one of the more basic inherited polymorphic relationships:
>>
>>
>> **Models Library**
>>
>> class Foo(models.Base):
>>
>> __tablename__ = "foo"
>> id = Column(Integer, primary_key=True)
>> type = Column(String)
>> foo_bar_id = Column(Integer, ForeignKey("foo_bar.id"))
>> foo_bar = relationship(Foo, backref=backref("foos"))
>>
>> __mapper_args__ = {"polymorphic_on": type}
>>
>>
>> class Bar(Foo):
>>
>> __mapper_args__ = {"polymorphic_identity": "bar"}
>>
>>
>> class FooBar(models.Base):
>>
>> __tablename__ = "foo_bar"
>> id = Column(Integer, primary_key=True)
>>
>>
>> **Main Repository**
>>
>> from separate_library.models import models, Foo as BaseFoo, Bar as
>> BaseBar, FooBar as BaseFooBar
>>
>>
>> class Foo(BaseFoo):
>>
>> @classmethod
>> def custom_create_method(cls, **kw):
>> foo_obj = cls(**kw)
>>
Re: [sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
On 06/03/2016 02:44 PM, Angie E wrote:
Rather than creating mixin classes that models inherit from, I have a
use case that requires me to configure classes the other way around. The
classes that would normally be mixin classes need to be the classes that
inherit from the models as well as the class that model objects are
created from. This is because the models and the mapper configurations
are in an external library from the main repository. I need to pass in
the host for the engine from the main repository to the models library
before any of the models are loaded so they can load with the
declarative base already configured.
I hope you are using reflection for these models, otherwise there's no
reason to have a depedency on the Engine for the model declaration.
After the engine information is
passed in, the session, Base class, and everything is created within a
sort of base class that the models inherit from. Here is a simplified
example:
class SQLAlchemyBase(object):
metadata = None
Session = None
Base = object
sessionfactory = sessionmaker()
def initialize(self, host):
engine = create_engine(host)
self.metadata = MetaData(bind=engine)
self.Session = scoped_session(self.sessionfactory)
self.Base = declarative_base(metadata=self.metadata)
models = SQLAlchemyBase()
(The models inherit from models.Base)
So the SQLAlchemyBase will be imported into the main repository, the
initialize method will be called, passing in the host for the engine,
and the models can then be imported.
Looks like no reflection taking place. I'd do away with the
MetaData(bind=engine), and just have the engine as part of the
sessionmaker(), and the sessionmaker() here also doesn't need to have
anything to do with the "library", if the "library" is just defining
model classes.
The "bound metadata" pattern is highly discouraged in modern SQLAlchemy
because it leads to this kind of confusion, e.g. that one needs an
Engine in order to declare models. You don't.
The main repository has its own
classes with the same names as the models and have additional methods
that a normal mixin class would have to extend functionality. However, I
am unable to create model objects using the classes in the main
repository because I can't get the mappers to play nice with this
unusual inheritance that extends from the external models library.
Additionally, in the models library, there are models that have multiple
levels of inherited polymorphic relationships. Here is an example that
is similar one of the more basic inherited polymorphic relationships:
**Models Library**
class Foo(models.Base):
__tablename__ = "foo"
id = Column(Integer, primary_key=True)
type = Column(String)
foo_bar_id = Column(Integer, ForeignKey("foo_bar.id"))
foo_bar = relationship(Foo, backref=backref("foos"))
__mapper_args__ = {"polymorphic_on": type}
class Bar(Foo):
__mapper_args__ = {"polymorphic_identity": "bar"}
class FooBar(models.Base):
__tablename__ = "foo_bar"
id = Column(Integer, primary_key=True)
**Main Repository**
from separate_library.models import models, Foo as BaseFoo, Bar as
BaseBar, FooBar as BaseFooBar
class Foo(BaseFoo):
@classmethod
def custom_create_method(cls, **kw):
foo_obj = cls(**kw)
models.session.add(foo_obj)
models.session.flush()
class Bar(BaseBar):
pass
class FooBar(BaseFooBar):
pass
The original error I was getting was something like this:
"InvalidRequestError: One or more mappers failed to initialize - can't
proceed with initialization of other mappers. Original exception was:
Multiple classes found for path "Foo" in the registry of this
declarative base. Please use a fully module-qualified path."
that only happens if someone is using a string name inside of
relationship(), like this:
foobars = relationship("Foo")
If the "library" is doing that, and you can't change it, easy solution,
use a different name for your "Foo" that's also in the 3rd party
library. Or declare your classes against a different base:
Base = declarative_base()
class Foo(other_package.Foo, Base):
# ...
class Bar(other_package.Bar, Base):
# ...
I'm not 100% sure that will work but there's probably a way to make that
work.
So I tried putting the full path in the relationships. Then it started
giving me an error like this:
oh, OK, then you're fine there.
"FlushError: Attempting to flush an item of type as a member of collection "FooBar.foos".
Expected an object of type or a
polymorphic subclass of this type. If
is a subclass of , configure mapper
"Mapper|Foo|foos" to load this subtype polymorphically, or set
enable_typechecks=False to allow any subtype to be accepted for flush.
Well, when this relationship loads, you'd like it to return a list of
main_module.models.Foo objects and not separate_library.models.Foo.
Your model here needs to have a
[sqlalchemy] Is there a way to create custom classes that inherit from sqlalchemy models in external library?
Rather than creating mixin classes that models inherit from, I have a use
case that requires me to configure classes the other way around. The
classes that would normally be mixin classes need to be the classes that
inherit from the models as well as the class that model objects are created
from. This is because the models and the mapper configurations are in an
external library from the main repository. I need to pass in the host for
the engine from the main repository to the models library before any of the
models are loaded so they can load with the declarative base already
configured. After the engine information is passed in, the session, Base
class, and everything is created within a sort of base class that the
models inherit from. Here is a simplified example:
class SQLAlchemyBase(object):
metadata = None
Session = None
Base = object
sessionfactory = sessionmaker()
def initialize(self, host):
engine = create_engine(host)
self.metadata = MetaData(bind=engine)
self.Session = scoped_session(self.sessionfactory)
self.Base = declarative_base(metadata=self.metadata)
models = SQLAlchemyBase()
(The models inherit from models.Base)
So the SQLAlchemyBase will be imported into the main repository, the
initialize method will be called, passing in the host for the engine, and
the models can then be imported. The main repository has its own classes
with the same names as the models and have additional methods that a normal
mixin class would have to extend functionality. However, I am unable to
create model objects using the classes in the main repository because I
can't get the mappers to play nice with this unusual inheritance that
extends from the external models library. Additionally, in the models
library, there are models that have multiple levels of inherited
polymorphic relationships. Here is an example that is similar one of the
more basic inherited polymorphic relationships:
**Models Library**
class Foo(models.Base):
__tablename__ = "foo"
id = Column(Integer, primary_key=True)
type = Column(String)
foo_bar_id = Column(Integer, ForeignKey("foo_bar.id"))
foo_bar = relationship(Foo, backref=backref("foos"))
__mapper_args__ = {"polymorphic_on": type}
class Bar(Foo):
__mapper_args__ = {"polymorphic_identity": "bar"}
class FooBar(models.Base):
__tablename__ = "foo_bar"
id = Column(Integer, primary_key=True)
**Main Repository**
from separate_library.models import models, Foo as BaseFoo, Bar as BaseBar,
FooBar as BaseFooBar
class Foo(BaseFoo):
@classmethod
def custom_create_method(cls, **kw):
foo_obj = cls(**kw)
models.session.add(foo_obj)
models.session.flush()
class Bar(BaseBar):
pass
class FooBar(BaseFooBar):
pass
The original error I was getting was something like this:
"InvalidRequestError: One or more mappers failed to initialize - can't
proceed with initialization of other mappers. Original exception was:
Multiple classes found for path "Foo" in the registry of this declarative
base. Please use a fully module-qualified path."
So I tried putting the full path in the relationships. Then it started
giving me an error like this:
"FlushError: Attempting to flush an item of type as a member of collection "FooBar.foos". Expected
an object of type or a polymorphic
subclass of this type. If is a subclass of
, configure mapper "Mapper|Foo|foos"
to load this subtype polymorphically, or set enable_typechecks=False to
allow any subtype to be accepted for flush.
Essentially, the main problem is getting the classes in the main module to
point to and act like the model classes. For example, when I try to create
relationships, it says it expected an object of type
'separate_library.models.Foo' instead of 'main_module.models.Foo'.
Additionally, in the polymorphic relationships, I can't get the
polymorphic_identity to populate for the polymorphic_on column. For
example, Bar in the main repository will have the 'type' column empty when
the object is initially created.
One idea I tried was to add a metaclass to the declarative base in the
models library and modify the mappers in the __init__ method during their
initialization. I made progress this way, but haven't gotten it to work
completely.
Sorry for the complex explanation, but this is a complex problem. I am not
able to change anything about the models or the use case, unfortunately. I
have to work within these constraints. If anyone can offer ideas on how to
configure the mappers for the classes in the main repository to act like
the models in the model library, I would be very grateful.
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sqlalchemy+unsubscr...@googlegroups.com.
To post to this group, send email to
