before_destroy callback not stopping record from being deleted

In Rails 5 you have to throw :abort otherwise it won’t work. (even returning false)

Also, you should add prepend: true to the callback, to make sure it runs before the dependent: :destroy on the parent models.

Something like this should work:

class Something < ApplicationRecord

  before_destroy :can_destroy?, prepend: true

  private

  def can_destroy?
    if model.something?
      self.errors.add(:base, "Can't be destroy because of something")
      throw :abort
    end
  end
end