On Oct 25, 2010, at 3:57 PM, Michael Bayer wrote: > > On Oct 25, 2010, at 2:19 PM, Mark Erbaugh wrote: > >> Does SA maintain a usable unique identifier for newly added child records >> before the data is committed? >> >> I have a mapping of a one-many relationship using a foreign key. The detail >> (many side) records are in an instrumented list. I need to relate the items >> in this list to rows in an user interface object (a ttk.Treeview object). >> The detail table has a primary key that is maintained by SA, but until the >> data graph has been committed to the database, the corresponding fields >> detail objects are None. >> >> I can't just use the position of the detail item in the instrumented list >> because it is possible that the user can add and delete rows. The Treeview >> object does not re-use row identifiers for rows that have been deleted, so >> after the user has added and deleted detail rows, the Treeview rows will not >> match the instrumented list rows. > > the ORM uses Python object identity to maintain associations before foreign > key / primary key identifiers are assigned. So you could either associate > your user interface objects directly with the related objects, or with their > identity via a dictionary, otherwise if you need something that is durable > beyond the scope of a single Session you'd need to assign a unique identifier > (uuid.uuid4() is a good choice for this) or issue flush() so that primary key > ids are available.
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