I would like to get what I described in the subject: attach an event
listener that will execute once after current transaction's successful
commit (analogue to django's on_commit
<https://docs.djangoproject.com/en/1.9/topics/db/transactions/#django.db.transaction.on_commit>
).
If current transaction rolls back, the event listener(s) should be
discarded.
I have tried using `event.listens_for(sess, 'after_commit', once=True)`,
but probably as expected it will execute the callback if session continues
to be used after rollback. Here is a complete source that you can play
around with:
from sqlalchemy import Column, Integer, create_engine, event
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(bind=engine)
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
Base.metadata.create_all(engine)
sess = Session()
sess.add(User(id=1))
sess.commit()
@event.listens_for(sess, 'after_commit', once=True)
def foo(session):
print("shouldn't be called since the transaction will be rolled back!")
sess.add(User(id=1))
try:
sess.commit()
except:
sess.rollback()
sess.add(User(id=2))
sess.commit() # event callback will be called here
There is also an `after_transaction_end` event, but unfortunately I have
not managed to bend it to my needs as well: 1) I haven't found public API
to determine the transaction state when the callback executes 2) If an
event listener is attached in a subtransaction, the callback will get
called when the subransaction commits, while I'd like to the callback to
only get called when the 'outermost' transaction commits successfully.
Greatly appreciate any help.
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