ruby - Rails: Validate only on create, or on update when field is not blank

Question

How can I restrict a Rails validation to check only on create OR when the field isn't blank? I'm creating a user settings page for an app I'm working on and the problem is that, when updating using the parameters provided by the form, the settings will only save when both a password and password confirmation are present. I would like these password fields to validate on create no matter what, but only on update when they are provided.

question from:https://stackoverflow.com/questions/24279948/rails-validate-only-on-create-or-on-update-when-field-is-not-blank

Answer 1

If you want to allow blank values use: allow_blank with validates.

class Topic < ActiveRecord::Base
  validates :title, length: { is: 5 }, allow_blank: true
end

If you want to validate only on create, use on with validates.

class Topic < ActiveRecord::Base
  validates :email, uniqueness: true, on: :create
end

To cover your case:

class Topic
  validates :email, presence: true, if: :should_validate?

  def should_validate?
    new_record? || email.present?
  end
end