> -----Original Message----- > From: sqlalchemy@googlegroups.com > [mailto:sqlalch...@googlegroups.com] On Behalf Of Raf Geens > Sent: 25 August 2010 16:48 > To: sqlalchemy@googlegroups.com > Subject: Re: [sqlalchemy] Session.merge and multiple databases > > > On 25/08/2010 17:15, Michael Bayer wrote: > > On Aug 25, 2010, at 10:50 AM, Raf Geens wrote: > > > >> Hi, > >> > >> I have a sqlite database A and a MySQL database B which > share the same > >> schema, where I want to synchronize the contents of > certain tables in > >> A with those in B at certain times. Except for the > synchronizing step > >> the contents on A's side don't change, while those on B's > side might. > >> > >> I'm trying to do this using Session.merge, which works if the row > >> doesn't exist yet in A, or does but hasn't changed in B. If it has > >> changed in B, I get a ConcurrentModificationError when the merge is > >> flushed. > > can't reproduce in 0.5.6 nor in 0.6.3, so a full test > script that reproduces will be needed. Alternatively, you > might want to look at your SQL output and see what primary > key is attempting to be updated: > > > Thanks for the quick reply. I've looked at the SQL output of the last > commit and it appears to match on the correct primary key. > However, the > Individual has a version_id_col defined in the mapper, and > it's trying > to match on the wrong value there, which seems to cause the update to > fail. I'll try to reproduce it in a full script. > > Raf
The version_id_col is likely not to work - the whole point of the column is that SA adds the current version to the WHERE clause, and then checks to see if any rows were updated. If they were, the object was still at the same version that SA loaded from the database. If no rows were updated, it assumes it was because someone else modified the object and incremented the version number (hence the ConcurrentModificationError). SA increments the version number every time a change to the object is flushed to the database. So when your object is modified in B, the version number no longer matches the version in A and no rows match the criteria. I don't know how you fix this if you want to continue using the version_id_col feature - is there any chance that you could do without it (perhaps by implementing similar functionality in a SessionExtension which only gets attached to the primary session)? Simon -- 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.
