Validation of Shouts

Ruby on Rails Intermediate Rails Tutorial
5

I spent some time yesterday figuring out a solution to this problem so I thought I might as well post it here.

The problem is that validations run before either record is saved, so there won’t ever be a content_id when a new shout is being validated. The answer I came up with was to create a custom validator to check content.valid?, like so:

class TextShout < ActiveRecord::Base
  validates :body, presence: true
end

class Shout < ActiveRecord::Base
  belongs_to :user, required: true
  belongs_to :content, polymorphic: true, required: true, dependent: :destroy
  validate :content_must_be_valid
  default_scope { order(created_at: :desc) }

  protected
  def content_must_be_valid
    if content && content.invalid?
      content_errors = content.errors.full_messages.join(", ")
      errors.add(:content, "not valid: #{ content_errors }")
    end
  end
end

Works for me. Would love to know if there’s a better way, though.