This is insanely helpful - thank you Michael. I'm going to pass the
dbsession into the class method for now but look into a service layer.
On Monday, January 6, 2020 at 2:56:28 PM UTC-6, Michael Merickel wrote:
>
> This is a super common complaint from people and it doesn't have a single
> definitive solution. There are a couple handy tricks:
>
> 1. If your classmethod receives any managed objects, you can get a
> reference to the session from the object itself. For example
> ``sqlalchemy.orm.object_session(user)``.
>
> 2. The easy answer when the above doesn't work is to pass the dbsession
> into the class method.
>
> After this - if still not satisfied - are some hacky things you can do:
>
> 1. Stop using classmethod approaches and instead put in a real service
> layer. This has tons of benefits, see something like pyramid_services for
> more information about this. This approach will allow you to bind the whole
> service to a dbsession, and no longer need to pass it around at all.
>
> 2. Define a helper to grab the session from the request threadlocal.
> Something like ``get_current_dbsession = lambda:
> get_current_request().dbsession``. Then import that and use it via
> ``dbsession = get_current_dbsession()``.
>
> The threadlocal approach above has some downsides but is still better than
> using a scoped session. Allowing the request to seep into and infect your
> data model is a little wonky and makes your model code less reusable
> outside of Pyramid. Even if you are okay with that, something like
> ``get_current_dbsession().query()`` is going to be better than
> ``scoped_session.query()`` because it's more explicitly a value that
> changes over time versus the magic scoped session object proxy.
>
> In my own apps I use all the approaches mentioned above except the
> threadlocal one.
>
> - Michael
>
> On Mon, Jan 6, 2020 at 2:37 PM Kate Boelhauf <ka...@katimari.com
> <javascript:>> wrote:
>
>> A little background - I'm updating my entire site and used a cookiecutter
>> as referenced in Pyramids docs to do so. I am using sqlalchemy.
>>
>> It has a db session as a request method. This works perfectly for me in
>> all of my views. However, I have class methods in my models that need to
>> access a session. I can't figure out a way to access the session that the
>> cookiecutter set up in models.py so I reverted to creating a separate
>> session using
>> scoped_session(sessionmaker(extension=ZopeTransactionExtension())) and
>> importing it into my model and using the request session in my views.
>>
>> This just seems wrong - am I approaching this wrong?
>>
>> Below is the model.py file that the cookiecutter created:
>>
>> from sqlalchemy import engine_from_config
>> from sqlalchemy.orm import sessionmaker
>> from sqlalchemy.orm import configure_mappers
>> import zope.sqlalchemy
>>
>> # import or define all models here to ensure they are attached to the
>> # Base.metadata prior to any initialization routines
>> from .mymodel import MyModel # flake8: noqa
>>
>> # run configure_mappers after defining all of the models to ensure
>> # all relationships can be setup
>> configure_mappers()
>>
>>
>> def get_engine(settings, prefix='sqlalchemy.'):
>> return engine_from_config(settings, prefix)
>>
>>
>> def get_session_factory(engine):
>> factory = sessionmaker()
>> factory.configure(bind=engine)
>> return factory
>>
>>
>> def get_tm_session(session_factory, transaction_manager):
>> """
>> Get a ``sqlalchemy.orm.Session`` instance backed by a transaction.
>>
>> This function will hook the session to the transaction manager which
>> will take care of committing any changes.
>>
>> - When using pyramid_tm it will automatically be committed or aborted
>> depending on whether an exception is raised.
>>
>> - When using scripts you should wrap the session in a manager yourself.
>> For example::
>>
>> import transaction
>>
>> engine = get_engine(settings)
>> session_factory = get_session_factory(engine)
>> with transaction.manager:
>> dbsession = get_tm_session(session_factory,
>> transaction.manager)
>>
>> """
>> dbsession = session_factory()
>> zope.sqlalchemy.register(
>> dbsession, transaction_manager=transaction_manager)
>> return dbsession
>>
>>
>> def includeme(config):
>> """
>> Initialize the model for a Pyramid app.
>>
>> Activate this setup using ``config.include('tutorial.models')``.
>>
>> """
>> settings = config.get_settings()
>> settings['tm.manager_hook'] = 'pyramid_tm.explicit_manager'
>>
>> # use pyramid_tm to hook the transaction lifecycle to the request
>> config.include('pyramid_tm')
>>
>> # use pyramid_retry to retry a request when transient exceptions occur
>> config.include('pyramid_retry')
>>
>> session_factory = get_session_factory(get_engine(settings))
>> config.registry['dbsession_factory'] = session_factory
>>
>> # make request.dbsession available for use in Pyramid
>> config.add_request_method(
>> # r.tm is the transaction manager used by pyramid_tm
>> lambda r: get_tm_session(session_factory, r.tm),
>> 'dbsession',
>> reify=True
>> )
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>> .
>>
>
>
> --
>
> Michael
>
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