Proposal: Convenience method to skip field validation when not changing the field

I’m working on an old, large rails codebase.

Recently, I needed to add a new validation to our users table, requiring something be entered in the name field.

However, there were many records which didn’t have anything in this field, and that would mean they couldn’t make unrelated changes to their user record (e.g. reset their passwords) as the whole record was invalid.

I have added the following snippet to my ApplicationRecord:

  def self.validates_new_and_changed(*fields, opts) do |field|
      validates field, opts.merge(on: :create)
      validates field, opts.merge(if: "#{field}_changed?".to_sym)

This is short and solves my problem, but I think Rails validations would benefit more generally from having a straightforward way to only run field validations when the field changes.

I’d envisage an API like

validates :name, :encrypted_password, presence: true, on: :create_or_field_changed

This new option for the on parameter would mean that for existing records, changes to the encrypted_password field would not generate validation errors on the name field unless that was also changed.