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.
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]
> <javascript:>> 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. See http://stackoverflow.com/help/mcve for a full
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>
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> >> > The Python SQL Toolkit and Object Relational Mapper
> >> >
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> >
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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