On Thu, May 16, 2019 at 4:26 PM Tony Cao <[email protected]> wrote: > > Ohh I see thanks for the help! > > And just to confirm on the onupdate front, is it not possible to return the > current value of the object being updated? It's ok to emit an extraneous > update if the value doesn't change.
inside the onupdate handler you can see the current statement and the parameters in the context, as far as the "a_1" thing, the parameters for the columns being SET should be the same keys as the column itself, it's the WHERE clause where you'd see the underscore thing happening. show me what you get if you want to work with that. > > On Wednesday, May 15, 2019 at 5:30:06 PM UTC-7, Mike Bayer wrote: >> >> On Wed, May 15, 2019 at 6:10 PM Tony Cao <[email protected]> wrote: >> > >> > I mean query.update(). >> > >> > Ah our goal was to make it so the update in question happened >> > automatically without the developer having to explicitly specify it - in >> > that case both obj.attr = x and obj_class.query.update({obj.attr: x}) >> > should both trigger an update to obj.attr_modified. That's why I initially >> > asked about onupdate, as it is triggered for both cases. >> >> >> for query.update() you can use the before_compile_update() and modify >> the context.values dictionary in place to affect the UPDATE statement >> generated by query.update(). See >> https://docs.sqlalchemy.org/en/13/orm/events.html?highlight=before_compile_update#sqlalchemy.orm.events.QueryEvents.before_compile_update. >> Additional detail regarding .values will be up within 30 minutes. >> >> >> > >> > >> > On Wednesday, May 15, 2019 at 2:38:19 PM UTC-7, Mike Bayer wrote: >> >> >> >> Bulk query updates, you mean, query.update() ? Or >> >> session.bulk_update_mappings() ? In both cases you are >> >> programatically providing the VALUES clause, so you know from your own >> >> data what the UPDATE statement will be. >> >> >> >> >> >> >> >> On Wed, May 15, 2019 at 4:14 PM Tony Cao <[email protected]> wrote: >> >> > >> >> > Ah but it also looks like the before_update event isn't triggered when >> >> > doing bulk query updates, which we'd like to also update on. Is there a >> >> > way to track those? >> >> > >> >> > On Wednesday, May 15, 2019 at 10:38:24 AM UTC-7, Mike Bayer wrote: >> >> >> >> >> >> you can inspect() the object and look at >> >> >> inspect(obj).attrs['some_attr'].history >> >> >> >> >> >> https://docs.sqlalchemy.org/en/13/orm/internals.html#sqlalchemy.orm.state.AttributeState >> >> >> >> >> >> >> >> >> On Wed, May 15, 2019 at 1:14 PM Tony Cao <[email protected]> wrote: >> >> >> > >> >> >> > Hi, >> >> >> > >> >> >> > Thanks for the response! I also tried looking into before_update, >> >> >> > but is there a recommended way to figure out what columns are being >> >> >> > updated from that event? I had found this post >> >> >> > (https://stackoverflow.com/questions/15642286/how-can-i-get-a-sqlalchemy-orm-objects-previous-state-after-a-db-update) >> >> >> > that suggests looking at the history of the attribute state - is >> >> >> > there a better way? >> >> >> > >> >> >> > On Wednesday, May 15, 2019 at 7:55:44 AM UTC-7, Mike Bayer wrote: >> >> >> >> >> >> >> >> On Mon, May 13, 2019 at 4:18 PM Tony Cao <[email protected]> >> >> >> >> wrote: >> >> >> >> > >> >> >> >> > Hi all, >> >> >> >> > >> >> >> >> > Is there way to use Column.onupdate conditionally? For example, >> >> >> >> > say I have: >> >> >> >> > >> >> >> >> > class A(Base): >> >> >> >> > foo = Column(String) >> >> >> >> > bar = Column(String) >> >> >> >> > foo_updated = Column(DateTime, onupdate=update_fn) # Should >> >> >> >> > only update when foo is updated >> >> >> >> > >> >> >> >> > def update_fn(context): >> >> >> >> > if ...: # How can I check if only foo was updated? >> >> >> >> > return datetime.now() >> >> >> >> > else: >> >> >> >> > return ... # How can I say to not update? >> >> >> >> > >> >> >> >> > Is there a way to define update_fn to only update foo_updated >> >> >> >> > when foo changes? I can look at context.get_current_parameters() >> >> >> >> > to see what columns are being used in the compiled statement, but >> >> >> >> > it doesn't explicitly say which columns are the ones actually >> >> >> >> > being updated; for example, if I have >> >> >> >> > >> >> >> >> > A.query.filter(A.bar == 'test').update({A.foo: 'new'}, >> >> >> >> > synchronize_session=False) >> >> >> >> > >> >> >> >> > then context.get_current_parameters will return a dict with keys >> >> >> >> > for both 'bar' and 'foo', although it looks like it suffixes the >> >> >> >> > filter param with a '_1' - is that something I can rely on to >> >> >> >> > know if a column is used as a filter instead of an update? And >> >> >> >> > beyond that, is there a way I can specify to not update the >> >> >> >> > column? >> >> >> >> > >> >> >> >> > Alternatively, is there another approach recommended to doing >> >> >> >> > this? >> >> >> >> >> >> >> >> the most common way is to use the ORM level before_update event: >> >> >> >> >> >> >> >> https://docs.sqlalchemy.org/en/13/orm/events.html?highlight=before_update#sqlalchemy.orm.events.MapperEvents.before_update >> >> >> >> >> >> >> >> there's also before_execute() at the Core level, but before the >> >> >> >> UPDATE >> >> >> >> statement is even written, e.g. at the ORM level, is the best way. >> >> >> >> Once you are in the onupdate Python function, you have to return a >> >> >> >> value, as this occurs well after the UPDATE statement has been >> >> >> >> compiled. >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> > >> >> >> >> > Thanks! >> >> >> >> > >> >> >> >> > -- >> >> >> >> > 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. 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