when you're using an event such as before_flush() to check on attributes.get_history() so that you can see that a new "version" needs to be inserted into a version table, you need the old value of the attribute in order to compare. see the versioned_history example.
On Mar 22, 2014, at 4:34 PM, Bao Niu <niuba...@gmail.com> wrote: > In the documentation for sqlalchemy.orm.column_property, there is a section > explaining the *active_history* flag. It is very terse. I think it is very > useful but just cannot think of a scenario where I would ever want to use > *previous* value when I'm setting a new value. Could someone use plain > language to explain it a bit more? Thanks. > > (I sometimes find reading SA documentations is like reading Bible, you know > the content is good for you, but you cannot easily figure out how. Group > study really helps:) > > -- > 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 sqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at http://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. -- 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 sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
