How to detect attribute changes from model?

ruby-on-rails

Solution

You should look at ActiveModel::Dirty module. You should be able to perform following actions on your `Claim` model:

claim.status_changed?  # returns true if 'status' attribute has changed
claim.status_was       # returns the previous value of 'status' attribute
claim.status_change    # => ['old value', 'new value'] returns the old and 
                       # new value for 'status' attribute

claim.name = 'Bob'
claim.changed # => ["name"]
claim.changes # => {"name" => ["Bill", "Bob"]}

Problem

I'd like to create a callback function in rails that executes after a model is saved. I have this model, Claim that has a attribute 'status' which changes depending on the state of the claim, possible values are pending, endorsed, approved, rejected The database has 'state' with the default value of 'pending'. I'd like to perform certain tasks after the model is created on the first time or updated from one state to another, depending on which state it changes from. My idea is to have a function in the model: ``` after_save :check_state def check_state # if status changed from nil to pending (created) do this # if status changed from pending to approved performthistask end ``` My question is how do I check for the previous value before the change within the model?

Original source