To consistently reproduce the error, the object needs to have changed
before accessing the relationship attribute:
import random
games = session.query(Game)
game = [g for g in games][0]
game.status = 'something_{}'.format(random.randint(0,100)) # Change made
court = game.court # StaleDataError if another processes has updated game
as well
session.add(game)
Running the above code at the same time results in the consistent
StaleDataError
On Friday, August 16, 2019 at 2:18:05 PM UTC-4, Vinit Shah wrote:
>
> I have code that looks like the following:
>
> games = session.query(Game)
> game = [g for g in games][0]
> court = game.court # StaleDataError
> game.
> session.add(game)
>
> Game looks like:
>
> class Game(Base):
> __tablename__ = "Games"
> id = Column(Integer, primary_key=True)
> courtId = Column('courtId', Integer, ForeignKey('Courts.id'))
> courtId = Column('courtId', Integer, ForeignKey('Courts.id'))
> court = relationship(Court, foreign_keys=[courtId], backref="games")
> revision = Column(Integer, nullable=False)
>
> __mapper_args__ = {
> 'version_id_col': revision
> }
>
>
> I've found that this error occurs when another process has updated the
> same row, which makes sense, since that is the purpose of the
> version_id_col.
> In the contrived example above, it's been difficult to reproduce the
> error. In production, I have found this happens consistently, so long as
> another process has updated the same Game row.
>
> I can easily wrap a "try/except" around where "court" is accessed from
> "game", but I'm curious as to why an UPDATE statement happens there in the
> first place.
>
> Below is the stacktrace:
>
> court = game.court
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py",
>
> line 243, in __get__
> return self.impl.get(instance_state(instance), dict_)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py",
>
> line 602, in get
> value = self.callable_(state, passive)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/strategies.py",
>
> line 634, in _load_for_state
> session, state, primary_key_identity, passive)
> File "<string>", line 1, in <lambda>
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/strategies.py",
>
> line 727, in _emit_lazyload
> primary_key_identity)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/ext/baked.py",
> line 570, in _load_on_pk_identity
> result = list(bq.for_session(self.session).params(**params))
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/ext/baked.py",
> line 410, in __iter__
> self.session._autoflush()
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/session.py",
> line 1493, in _autoflush
> self.flush()
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/session.py",
> line 2313, in flush
> self._flush(objects)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/session.py",
> line 2440, in _flush
> transaction.rollback(_capture_exception=True)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
>
> line 66, in __exit__
> compat.reraise(exc_type, exc_value, exc_tb)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/session.py",
> line 2404, in _flush
> flush_context.execute()
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/unitofwork.py",
>
> line 398, in execute
> rec.execute(self)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/unitofwork.py",
>
> line 563, in execute
> uow
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/persistence.py",
>
> line 177, in save_obj
> mapper, table, update)
> File
> "/home/prism/.local/lib/python2.7/site-packages/sqlalchemy/orm/persistence.py",
>
> line 797, in _emit_update_statements
> (table.description, len(records), rows))
> StaleDataError: UPDATE statement on table 'Games' expected to update 1
> row(s); 0 were matched.
>
> Environment:
> Python 2.7
> SQLAlchemy 1.3.0b1
> Oracle
>
>
--
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
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