On Wed, May 27, 2020, at 3:57 PM, Colton Allen wrote:
> Hello,
>
> I'm trying to automate a backref update. Basically, when a child model is
> inserted or updated I want the parent model's "updated_at" column to mutate.
> The value should be the approximate time the user-child-model was updated.
> The updated_at value would not have to match the created_at/updated_at value
> on the child. It would just need to mutate to a new time.
>
> class UserModel(db.Model):
> updated_at = db.Column(db.DateTime, default=db.now, onupdate=datetime.now)
>
>
> class UserChildModel(db.Model):
> user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
> user = db.relationship('UserModel', backref='children')
>
> user = UserModel()
> save(user)
> print(user.updated_at) # x
>
> child = UserChildModel(user_id=user.id)
> save(child)
> print(user.updated_at) # y (value changed)
>
> Hopefully this pseudocode is sufficient.
>
> I'm wondering if there is an option I can specify on the orm.relationship
> factory. Or will I need to define an event?
that could certainly be based on an event from the SQLAlchemy side. a very
straightforward one would be the before_insert / before_update / after_insert /
after_update suite of events, I would emit an UPDATE statement against the
parent table using the foreign key on the child row that's being
inserted/updated. Another approach would be a DB trigger.
the mapper level events are detailed at
https://docs.sqlalchemy.org/en/13/orm/events.html?highlight=before_insert#sqlalchemy.orm.events.MapperEvents.before_insert
the "connection" right there is where you'd run your update, like:
connection.execute(update(parent).values(updated_at=datetime.now()).where(parent.id
== inserted.parent_id))
>
> Thanks!
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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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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