Determine what attributes were changed in Rails after save callback

Question

I m setting up an after save callback in my model observer to send a notification only if the model s published attribute was changed from false to true  Since methods such as changed  are only useful before the model is saved  the way I m currently  and unsuccessfully  trying to do so is as follows   def before save blog     og published   blog published  end  def after save blog    if  og published    false and blog published     true     Notification send        end end   Does anyone have any suggestions as to the best way to handle this  preferably using model observer callbacks  so as not to pollute my controller code

User · Answer

For those who want to know the changes just made in an after_save callback:

Rails 5.1 and greater

model.saved_changes

Rails < 5.1

model.previous_changes

Also see: http://api.rubyonrails.org/classes/ActiveModel/Dirty.html#method-i-previous_changes

User · Answer

The  selected  answer didn t work for me  I m using rails 3 1 with CouchRest  Model  based on Active Model   The  changed  methods don t return true for changed attributes in the after update hook  only in the before update hook  I was able to get it to work using the  new   around update hook   class SomeModel  lt  ActiveRecord  Base   around update  send notification after change    def send notification after change     should send it   self published changed   amp  amp  self published    true      yield      Notification send      if should send it   end  end

User · Answer

Rails 5 1   Use saved change to published    class SomeModel  lt  ActiveRecord  Base   after update  send notification after change    def send notification after change     Notification send      if  saved change to published   amp  amp  self published    true    end  end   Or if you prefer  saved change to attribute   published    Rails 3   5 1     Warning      This approach works through Rails 5 1  but is deprecated in 5 1 and has breaking changes in 5 2   You can read about the change in this pull request    In your after update filter on the model you can use  changed  accessor  So for example   class SomeModel  lt  ActiveRecord  Base   after update  send notification after change    def send notification after change     Notification send      if  self published changed   amp  amp  self published    true    end  end   It just works

User · Answer

In case you can do this on before save instead of after save  you ll be able to use this   self changed   it returns an array of all changed columns in this record   you can also use   self changes   which returns a hash of columns that changed and before and after results as arrays

User · Answer

To anyone seeing this later on  as it currently  Aug  2017  tops google  It is worth mentioning  that this behavior will be altered in Rails 5 2  and has deprecation warnings as of Rails 5 1  as ActiveModel  Dirty changed a bit   What do I change   If you re using attribute changed  method in the after  -callbacks  you ll see a warning like      DEPRECATION WARNING  The behavior of attribute changed  inside of after callbacks will be changing in the next version of Rails  The new return value will reflect the behavior of calling the method after save returned  e g  the opposite of what it returns now   To maintain the current behavior  use saved change to attribute  instead   called from some callback at  PATH TO app models user rb 15    As it mentions  you could fix this easily by replacing the function with saved change to attribute   So for example  name changed  becomes saved change to name    Likewise  if you re using the attribute change to get the before-after values  this changes as well and throws the following      DEPRECATION WARNING  The behavior of attribute change inside of after callbacks will be changing in the next version of Rails  The new return value will reflect the behavior of calling the method after save returned  e g  the opposite of what it returns now   To maintain the current behavior  use saved change to attribute instead   called from some callback at  PATH TO app models user rb 20    Again  as it mentions  the method changes name to saved change to attribute which returns   old    new    or use saved changes  which returns all the changes  and these can be accessed as saved changes  attribute

User · Answer

You just add an accessor who define what you change  class Post  lt  AR  Base   attr reader  what changed    before filter  what changed     def what changed       what changed   changes         end    after filter  action on changes    def action on changes      what changed each do  change        p change     end   end end

User · Answer

you can add a condition to the after update like so   class SomeModel  lt  ActiveRecord  Base   after update  send notification  if   published changed         end   there s no need to add a condition within the send notification method itself

[ruby-on-rails] Determine what attributes were changed in Rails after_save callback?

Rails 5.1 and greater

Rails < 5.1

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