On Sep 21, 2010, at 7:04 PM, Michael Hipp wrote: > On 9/21/2010 7:31 AM, Michael Hipp wrote: >> I need to "empty" an item (row). I thought to do this: >> >> new = Item() # create a new empty object >> new.id_ = old.id_ # copy certain other fields also >> self.session.expunge(old) >> self.session.add(new) >> self.session.commit() >> >> But it seems SA still tries to save it with an INSERT. (I thought the >> presence >> of the PK was what determined that.) >> >> Is there some way to "blank" a record and save it back with the same PK and a >> few other select fields that need to be kept? > > I continue to play with this. It reads like 'merge' would do exactly what I > want, but I must be misunderstanding it. > http://www.sqlalchemy.org/docs/orm/session.html#merging > > Changing the 'session.add' line to 'session.merge' still produces > IntegrityError: duplicate key value violates unique constraint > > Trying it with and without the 'expunge' line just changes the error to > New instance ... conflicts with persistent instance > > Can anyone suggest an approach to "empty" a record?
new = Item() new.id = old.id new.some_foo = 'bar' new = session.merge(new) session.commit() the full primary key attributes of "new", above the single attribute "id", must be populated. If an integrity error is raised, this may suggest an INSERT is occuring, which you should verify by echoing SQL and then ensure that the primary key fields of "new" are fully filled in and that such a row actually exists, again echoing SQL should reveal a SELECT statement for the row and if echo='debug' you will see the row come back. If the integrity error is raised and the statement is observed to be an UPDATE, then you are updating a column to a value that is already present in some other row in the table, where the column has a UNIQUE constraint on it. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
