How to access Rails's 'can't be blank' error message?

Question

What's the API to access Rails's default can't be blank error message when validation :presence => true fails?

I have the model setup like this:

class TextDocument < Document
  validate :content_not_blank   # 'content' is an attribute

  private
    def content_not_blank
      if content.blank? 
        errors.add(:content, ....?) # I want to access 'can't be blank'
      end
    end
end

Answer 1

I18n.t('errors.messages.blank')

should give you what you want.

Answer 2

Assuming you're using standard yaml translations, you can find the file in ActiveModel

To override it you'd drop a file in your config/locales folder, e.g.:

en:
  errors:
    messages:
      blank: "can't be whatever your custom message"

Answer 3

You can just do it with the default method like this:

validates_presence_of(:content)

This will generate the right message (can't be blank) in the current local (if you setup your config/locales/ ..yml files

if you really want to write your own validator

errors.add(:content, I18n.translate(:blank))