How do you create a callback with an if statement for multiple changed fields in Ruby on Rails?

Question

I would like to create a before_save callback that only gets run if there have been changes to any (but not necessarily all) of the three fields (street, city,

Answer 1

Option One

You could create a method like:

def ok_to_run_test_method?
  street_changed? || something_changed? || something_else_changed?
end

and then use:

before_save :run_test_method, :if => :ok_to_run_test_method?

Note how :ok_to_run_test_method? is a symbol. Not sure if it was a typo or not but in your question you are actually calling a class method street_changed?.

Option Two

Modernise your callbacks a little bit and use the block-style syntax:

before_save do
  if street_changed? || something_changed? || something_else_changed?
    # whatever you currently have in #run_test_method
  end
end

Answer 2

You can do it in one line using a Proc:

class User
  before_save :run_test_method, :if => Proc.new { |u| u.street_changed? || u.city_changed? || u.state_changed? }

  ...
end

Answer 3

You can also use a lambda:

before_save :run_test_method, if: ->(u) {u.street_changed? || u.something_changed? || u.something_else_changed?}