Dirty Associations

[Chris O'Meara]

Hello,

I found an area where I don't totally understand the behavior of the dirty tracking feature in Active Record. It appears as though changes are tracked when I assign a persistent object (already has an id) to the association but not tracked when I assign a new record to the association.

Here's a test that highlights the difference:

http://gist.github.com/238283

Is the difference between the two usages intentional?

Thanks,
Chris

[Michael Koziarski]

> Is the difference between the two usages intentional?

Nope, looks like a side-effect of the implementation to me.


--
Cheers

Koz

[Matt Jones]

Poking around a little, it's completely an implementation side-effect,
and only appears in the exact case you've described. For instance,
assigning to a has_many doesn't show up in .changes either:

def test_changed_includes_new_record_assignments
album = Album.create! :title => "Give Up the Ghost"
album.artist = Artist.new :name => "Brandi Carlile"
assert album.changes.any?
end

In the belongs_to case in your example, note that the change does get
recorded fairly early (before the before_save callback is invoked), so
you're OK using the dirty tracking in callbacks / observers.

--Matt Jones

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