Rails session id is nil

I've got a Rails 2.3.5 application that I'm migrating to Rails 3.0.10 that's run into a problem with sessions.

Some code is failing during integration tests because the session has no id (request.session is an empty hash, and request.session_options[:id] is nil). We are currently using webrat, but the same thing happens with capybara and with standard rails helpers. Sessions do seem to be se开发者_如何学运维t up properly, since some of the integration tests have session ids. It looks like the session id is missing only in tests that don't log in before trying to access the session id (i.e. most of them).

I've tried switching the session backend (it's currently cookie based) to ActiveRecord, but that didn't help. I've created a new Rails 3.0.10 app, and it also has nil session ids. I've even dug into Rails's session handling, and it looks like there's no session id being generated on if a session is missing one.

Is this lack of session ids expected behavior that's documented somewhere? If it's a bug, is there a version of Rails that generates session ids properly?

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The only way I've seen how to solve this is to prime the sessions.

sid1 = session[:session_id]      
sid2 = request.session_options[:id]

However, if for some reason the session cookie is deleted, it can still happen.

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I tried that and no result. I also tried session[:foo] = 'bar' as I liked the way it looked better but still no result.

I rebooted and still no joy. Then I went into my browser settings and deleted my cookies. That fixed it. From this experience it appears a cookie can keep sessions from being forced. I had been changing class names and changing my database tables. Somehow I had corrupted my cookie.