Karl Smith wrote in post #978748: > Hmm, so you are saying I could use a multi-field index (:user_id, > :credit_card_number). Then, during inserts if a duplicate > :credit_card_number is attempted a ActiveRecord::StatementInvalid would > be > generated, thus giving me an indication to try another > credit_card_number. > > Sounds workable, but is it realistic?
Yes, this is really common in database design. There was a time when composite primary keys were common and this is how those were enforced to be unique. However, the use of the technique is not limited to composite keys. > >> http://www.postgresql.org/docs/8.1/static/sql-createsequence.html >> > I don't like that, but nice to know. Some databases use sequences exclusively for generating primary keys. As opposed to providing auto-incrmenting column types... Just FYI. >> My concern about locking the entire table would be that if something >> went wrong then you might end up in a state where your entire table is >> stuck in a locked state. I don't know for sure if that's an issue with >> PostgreSQL, but something to consider. >> > Which concerns me as well. > > >> > I like that idea. That way I'm only locking that sequence table. This > way I > could use row level (pessimistic) locking. > > So, have you are anyone else tried this? Yes, I have used this technique for generating serial sequences on a number of projects. And you are correct that row level locking is used to manage concurrent access. http://www.postgresql.org/docs/8.1/static/sql-select.html#SQL-FOR-UPDATE-SHARE -- Posted via http://www.ruby-forum.com/. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" 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/rubyonrails-talk?hl=en.
