How to perform model validation in rails?

Question

I have a rails application where Activity is one of the resources with the following attributes:

• status (recording the status of activity "in progress", "complete")
• start (date when activity started)
• end (date when activity ended)

I want to create a new record for activity with status "in progress", given there is no existing activity with the same status. I believe this can be done using model validation, but being new to rails I have no idea how.

Answer 1

If status is a enum you may do:

class Activity < ApplicationRecord
  enum status: [ :in_progress, :complete ]

  validates_uniqueness_of :status, if: :in_progress?
end

This validation restricts you have only one activity with in_progress status.

Also if status is a string you may do:

class Activity < ApplicationRecord
  validates_uniqueness_of :status, if: proc { |activity| activity.status == 'in_progress' }
end