On Wed, Feb 3, 2021, at 6:23 PM, Christian Henning wrote:
> Hi Mike,
>
> thanks for your advice! I'll make the changes.
>
> But let me ask you one thing. My classmethod create() is but more complex
> than I have posted. It's meant to catch IntegrityError so that unique
> constraints are enforced. Image a User table has a "unique" constraint on the
> name. When I try to create a user with the same name the create() would catch
> the exception and return the original user. I believe this only possible when
> all objects are committed to the database.
>
> class ModelBase:
>
> @classmethod
> def create(cls, session, **kwargs):
> obj = cls(**kwargs)
> try:
> obj.save(session)
> except IntegrityError:
> # print('HOLA - Integrity Error')
>
> session.rollback()
> obj = cls.find(session, **kwargs)
>
> return obj
>
> def save(self, session):
> session.add(self)
> session.commit()
>
> How would you solve the problem? Is there anything in the documentation?
yes, use a SAVEPOINT for that, so you can roll back to the savepoint and still
have the transaction continue:
https://docs.sqlalchemy.org/en/13/faq/sessions.html#but-why-does-flush-insist-on-issuing-a-rollback
so you can place in your method:
session.begin_nested():
session.add(obj)
try:
session.flush()
except IntegrityError:
session.rollback()
else:
session.commit()
>
> Thanks,
> Christian
>
>
>
>
>
> On Wednesday, February 3, 2021 at 5:12:30 PM UTC-5 Mike Bayer wrote:
>> __
>> the session.commit() method expires all attributes by default:
>>
>> https://docs.sqlalchemy.org/en/13/orm/session_basics.html#committing
>>
>> your code is organized in an unusual way such that transactions are being
>> committed inside of attribute assignment operations:
>>
>> jack.addresses.append(Address.create(session))
>>
>> We can expand this out as follows:
>>
>> addr = jack.addresses
>> address = Address()
>> session.add(address)
>> session.commit() # <--- expires all attributes on "jack", "address",
>> invalidates "addr"
>> attr.append(address) # <--- this is invalid, transaction was already
>> commited
>>
>> I would strongly advise keeping session scope manage external to the set of
>> operations you are performing. See
>> https://docs.sqlalchemy.org/en/13/orm/session_basics.html#when-do-i-construct-a-session-when-do-i-commit-it-and-when-do-i-close-it
>> for guidelines.
>>
>>
>> On Wed, Feb 3, 2021, at 2:27 PM, Christian Henning wrote:
>>> I don't understand why SQLAlchemy gives me the following warning:
>>>
>>> SAWarning: This collection has been invalidated.
>>> util.warn("This collection has been invalidated.")
>>>
>>> Here is a minimal code example:
>>>
>>> -----------------
>>> -----------------
>>>
>>> import sqlalchemy
>>> print(sqlalchemy.__version__)
>>>
>>> from sqlalchemy import create_engine
>>> from sqlalchemy import Column, Integer, ForeignKey
>>>
>>> from sqlalchemy.exc import IntegrityError
>>> from sqlalchemy.ext.declarative import declarative_base
>>>
>>> from sqlalchemy.orm import relationship
>>> from sqlalchemy.orm import sessionmaker
>>>
>>> Base = declarative_base()
>>>
>>> class ModelBase:
>>>
>>> @classmethod
>>> def create(cls, session, **kwargs):
>>> obj = cls(**kwargs)
>>> session.add(obj)
>>> session.commit()
>>>
>>> return obj
>>>
>>>
>>> class User(ModelBase, Base):
>>> __tablename__ = 'users'
>>>
>>> id = Column(Integer, primary_key=True)
>>>
>>> addresses = relationship("Address", order_by="Address.id",
>>> back_populates="user")
>>>
>>> class Address(ModelBase, Base):
>>> __tablename__ = 'addresses'
>>>
>>> id = Column(Integer, primary_key=True)
>>>
>>> user_id = Column(Integer, ForeignKey('users.id'))
>>>
>>> user = relationship("User", back_populates="addresses")
>>>
>>>
>>> engine = create_engine('sqlite:///:memory:', echo=False)
>>> Base.metadata.create_all(engine)
>>>
>>> Session = sessionmaker(bind=engine)
>>> session = Session()
>>>
>>> jack = User.create(session)
>>> jack.addresses.append(Address.create(session))
>>>
>>> -----------------
>>> -----------------
>>> I have tested the code with SQLAlchemy for 1.3.18 and 1.4.0b1. I'm using
>>> python 3.9.1
>>>
>>> When I rewrite the last few lines a bit the warning disappears. For
>>> instance:
>>>
>>> jack = User.create(session)
>>> a = Address.create(session)
>>> jack.addresses.append(a)
>>>
>>>
>>> Any insight is appreciated. I'm still learning.
>>>
>>> Thanks,
>>> Christian
>>>
>>>
>>>
>>> --
>>> SQLAlchemy -
>>> The Python SQL Toolkit and Object Relational Mapper
>>>
>>> http://www.sqlalchemy.org/
>>>
>>> To post example code, please provide an MCVE: Minimal, Complete, and
>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
>>> description.
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>>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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