Why do I get "Unknown validator: 'MessageValidator'"?

Question

I get this error

Unknown validator: 'MessageValidator'

I have no idea why I'm getting that.
What's wrong with my code?

validates :title,   
    :presence => true,   
    :uniqueness => true,   
    :length => { :maximum => 100 },
    :message => "Must be input and has to be less than 100 characters, and unique."

Answer 1

Try:

validates :title, 
          :presence => {:message => "Title can't be blank." },
          :uniqueness => {:message => "Title already exists."},
          :length => { :maximum => 100, :message => "Must be less than 100 characters"}

Answer 2

I assume you want the message to be when the length validation fails. You should be including message in that hash like:

validates :title,   
    :presence => true,   
    :uniqueness => true,   
    :length => { :maximum => 100, :message => "Must be less than 100 characters"}