Named Scope bug?

rubyonrails-talk
1

Hi guys, I'm having a hard time with a scope within an ActiveRecord model. Here's my class: https://gist.github.com/1622314

The scope is named "current" and should select records between two dates and here is what happens: https://gist.github.com/1622334

This is the output for a rails console session, it contains logging to the STDOUT so you'll see the executed SQL commands there.

Here's a quick explanation for that console output: Line 1 shows there's no Message record.

Line 4 creates a Message

Line 14 calls the "current" named scope that should fetch the recently created message and shows how this message is not retrieved.

However, if I exit the console and then re-enter the console, Message.current does retrieve the recently created record.

I'm using Rails 3.1.3 and Ruby 1.9.3-p0. It wasn't happening on Rails 3.0 and Ruby 1.9.2-p290

Any clues?

Thanks a lot in advance.

2

This is not really a bug, but more due to the way Ruby evaluates when things are executed.

scope :current, where("start <= ? AND expiration > ?", DateTime.now, DateTime.now)

The code does use the current date/time, but the catch is that it doesn't use the current date/time when the scope is called, but when the model is loaded. Meaning, when the console is loaded or the app is started. It never updates the date/time used for the scope once it's loaded.

You'll want to use a Proc or lambda in this scenario, so the scope always uses the current date/time when the scope is called.

    scope :current, Proc.new { where("start <= ? AND expiration > ?", DateTime.now, DateTime.now) }

That way, DateTime.now is only evaluated when the scope is called.
3

Hi Tim, Great point. That was, in fact, the problem.

Thanks a lot.