How to make sure a Rails Active Record model attribute value is set once but cannot be updated again - attr_readonly

Recently I had to work on a task to add updated_at and created_at timestamps to an existing model(and its related table) and the related service class was using upsert_all (for performance reasons) to create/update new instances of that model and that class required adding these timestamps.

The app is currently on Rails 6 and with Rails 6 there is no auto update to created_at and updated_at timestamps via an upsert_all(This has changed with Rails 7 - more here ).

One way of setting these timestamps for this model that uses the upsert_all command is to do it manually for each record by manually passing created_at and updated_at as one would normally pass other model attributes as part of strong params in a controller and it’s related create/update actions.

Setting the created_at and updated_at using Time.current was how we were setting these timestamps for record insertions of the model in question via upsert_all but how do we handle updates with Time.current as we we wouldn’t want the value of created_at to change to the current time when we update an existing record using upsert_all.

Solution: attr_readonly.

As in the docs: Attributes listed as readonly will be used to create a new record but update operations will ignore these fields.

Sample code usage:

class ModelBeingInsertedAndLaterUpdated < ApplicationRecord
  attr_readonly :created_at
end