Seeing what has changed in ActiveRecord

Rails
1

I have a callback (before_save) that I want to trigger only when
certain fields within a record have changed. For example given a user
record with ‘username’, ‘password’ and ‘date_of_birth’ I would like
the callback to do something only when the ‘username’ or ‘password’
changes or when the ‘date_of_birth’ changes from nil to something
real. For example, how would I write…

before_save :audit_changes

def audit_changes
if old.username != new.username
audit("The username has changed from #{old.username} to
#{new.username})
end

if old.password != new.password
audit(“The user has changed their password”)
end

if old.date_of_birth == nil and new.date_of_birth != nil
audit(“The user has finally set their date of birth”)
end
end

Now this is just a little example of what I want to do, don’t get hung
up on the example, but how can I write this?

2

On Mon, Jan 24, 2011 at 11:49 AM, Peter H.
[email protected] wrote:

if old.username != new.username
end

Now this is just a little example of what I want to do, don’t get hung
up on the example, but how can I write this?

Active Record has API for that:

http://api.rubyonrails.org/classes/ActiveModel/Dirty.html

so you basically could test whether username_changed?, for example.

The examples in AM::Dirty include the module by hand, but you don’t
need to do that in AR models.

3

Thank you, I’ve been googling away like crazy but forgot to use that
magic word DIRTY. Damn I knew it was available.

Thank you.