Thanks... that is very helpful. I could keep references to these. If I choose the apparently lazier route and set weak_identity_map=False, then does any other action besides explicitly expunging free this memory, such as when the session goes out of scope, I assume? Or do I need to carefully expunge them?
On Mar 4, 4:09 pm, Conor <conor.edward.da...@gmail.com> wrote: > Conor wrote: > > Kent wrote: > > >> I agree I shouldn't care, so maybe there is another way to attack my > >> problem. The reason I care is because I've extended the python object > >> with some auxiliary information that I need. After the refresh() in > >> this case, I still need access to that data that is tied to the > >> object, but not present in the database (it is transient data). If > >> sqla creates a new instance, I loose that data. > > >> Is there a better mechanism for doing that? > > > You need to either manually keep strong references to each object that > > has the auxiliary information or disable the weak identity map. See > >http://www.sqlalchemy.org/docs/05/session.html#frequently-asked-quest... > > or > >http://www.sqlalchemy.org/docs/05/session.html#frequently-asked-quest... > > for more information. > > That second link should > behttp://www.sqlalchemy.org/docs/05/session.html#session-attributes. Oops. > > >> On Mar 4, 3:38 pm, "Michael Bayer" <mike...@zzzcomputing.com> wrote: > > >>> refresh doesn't remove any objects from the session so its a matter of > >>> what is present in the session, not marked as dirty, and strongly > >>> referenced on the outside. if you're using refresh you shouldn't care > >>> about how it gets data back into the collection. > > >>> Kent wrote: > > >>>> What's strange is that I can't recreate the problem on more simple > >>>> stage. Every time I refresh() on the parent object, the list objects > >>>> remain the same. In other words, *sometimes* it behaves as I hope it > >>>> to (by apparently refreshing the list's objects) and *sometimes* if > >>>> throws them out and creates new ones. The mystery to me is what > >>>> determines when it will create new instances vs. refreshing the > >>>> existing ones? > > >>>> On Mar 4, 3:24 pm, "Michael Bayer" <mike...@zzzcomputing.com> wrote: > > >>>>> Kent wrote: > > >>>>>> If I use session.refresh(obj) to re-load an obj that has a one-to-many > >>>>>> relational property, the objects in the list are *replaced* instead of > >>>>>> *refreshed* if they already exist. > > >>>>>> Suppose department has a list of employees: > > >>>>>> suppose dept.employees = [ emp1, emp2 ] > > >>>>>> session.refresh(dept) > > >>>>>> the dept."employees" list's elements are replaced with new objects > >>>>>> instead of reusing those that existed and refreshing them. > > >>>>>> Is it possible to have those same objects re-used and simply refreshed > >>>>>> instead of replaced? > > >>>>> you can only turn off "refresh-expire" cascade, which will prohibit the > >>>>> operation from traveling into the child objects. the collection is > >>>>> still > >>>>> refreshed for obvious reasons, its one of the attributes on your mapped > >>>>> object. > > >>>>> To achieve your specified behavior, use session.refresh() given as its > >>>>> second argument the set of attribute names which are safe to be reloaded > >>>>> completely (in this case the scalars). Then for each uselist > >>>>> attribute, > >>>>> iterate the collection of each and call the desired version of > >>>>> session.refresh() for those. > > >>>>> This is an easy refresh() function to create in a generalized way by > >>>>> inspecting the class-level attributes of the incoming object. > > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
