validate_uniqueness_of question

rubyonrails-talk
1

Make a unique index in the database, and write this:

begin    ModelName.create rescue Exception => e    # interrogate e to determine what sort of failure it was    # and take the appropriate action. end

This is the right way to do this. Testing before insert doesn't work because it's possible that after you test, but before you insert, another process may have inserted a duplicate!

2

Bryan,

I think validates_uniqueness_of does have a "valid" place. It lets you keep your code DRY and works in 99.999% of the cases. It only fails in the very rare case where another insert occurs after one thread (or mongrel process) has checked for uniqueness. In that very rare case the db's unique index would catch it and the database would stay valid. The only side effect is that the app would render an error page to the user. I'm willing to bet that this would likely never happen until a site got really big, and in even then it would have to be the perfect storm.

3

I agree. If only the databases and their drivers provided these info in a more standard, accessible way. I tried parsing postgres contraint violation errors and it’s a real pain to deduce which table and columns were affected, especially since these messages are locale dependent and change between versions.

That said, a common way to introspect database errors in addition to tables + columns would be wonderful.

jeremy