On 10/13/2016 11:59 AM, Colton Allen wrote:
Hi all,
I have a primary model with a "before_update" event and a secondary
model with a foreign key to the primary model. When I create a
secondary model, the primary model's "before_update" event is triggered.
I believe this is because the backref is being updated. Can I prevent
this behavior?
class Primary(Model):
id = Column(Integer)
@event.listens_for(Primary, 'before_update')
def example(m, c, t):
print("I was triggered by a mapper update!")
class Secondary(Model):
primary_id = Column(ForeignKey)
primary = orm.relationship('Primary', backref='secondaries')
s = Secondary(primary_id=1)
session.add(s)
session.commit()
that example as written cannot invoke the before_update() event. There
is no reference to the Secondary.primary or Primary.secondaries
attributes in any way and they are not involved in the operation.
Feel free to provide a full MCVE that more accurately shows what you are
doing.
For the case where you append an object to a collection, it is necessary
that the primary key of the collection-holding object is copied into the
foreign key attributes of the related object, which counts as a change
event.
You might try to limit your event handler to look at the attributes
which changed that you might care about, for example:
@event.listens_for(B, 'before_update')
def example(m, c, t):
if inspect(t).attrs.x.history:
print("I was triggered by a mapper update!")
I was triggered by a mapper update!
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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
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