you'd want to put a unique constraint on your username column, then let the transaction fail, do a rollback(), report the username isn't available. If you'd like to do the rollback and then continue without losing other pending changes, you'd use begin_nested().
On Oct 31, 2010, at 3:35 PM, Guguscat wrote: > Hello, > > I am using SQLAlchemy in a Pylons project and I like it. > > However I am questioning about the best way to insert data into a > database. > > I have a User class mapping my user table which has a Column > 'username' which has a unique constraint. > > So I have a form to add a new user when I submit the form I query the > database to see if the 'username' is already being used. > > I think the way I'm doing it is not good in the case where I have two > people trying to add the same 'username' at the same time, I guess the > both queries will return an empty set then when comitting the sessions > one will go well and one will fail returning a 503 error to the user. > > So I would like instead of doing this try to flush the session and > catch the exception if any and find the error. > > I don't know which method is the best or if one method is wrong > furthermore I don't know enough about database systems and if they all > react the same way. > > Thanks for anyone who could give me more information about this. > > -- > 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. > -- 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.
