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 >> > description. >> > --- >> > You received this message because you are subscribed to the Google Groups >> > "sqlalchemy" group. >> > To unsubscribe from this group and stop receiving emails from it, send an >> > email to [email protected]. >> > To post to this group, send email to [email protected]. >> > Visit this group at https://groups.google.com/group/sqlalchemy. >> > To view this discussion on the web visit >> > https://groups.google.com/d/msgid/sqlalchemy/b66e89c9-6618-4600-9381-182fa101f5b6%40googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. > > -- > 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 > description. > --- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/sqlalchemy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy/f13c4205-1df5-49c5-8c91-3c97cd8d9b05%40googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- 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 description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/sqlalchemy. To view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy/CA%2BRjkXE_OVYtRUUZpbf-hfBvyuu%3D0%2BHUJSTps31EE186gskxLQ%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
