Question

,I need to validate a form field so it cannot be a specific string. For example if someone inputs “hello” into a text field and submits the form, how can I throw an error saying that particular string is not allowed? Is there a way to avoid doing this on the client side with javascript so I can keep the feel consistent?

validates_presence of :field_name, #condition here

Answer 1

you need to pass custom validation

INVALID_STRING = %W(string1, string2, string3, ... )
def valid_field_name    // valid_name
  if INVALID_STRING.include?(self.field_name)
    errors[:base] << "field_name you enter that not valid." unless self.field_name.blank?
  end
end

call this method

 validate:valid_field_name