image and video validation with paperclip

validates_attachment_presence :source
  validates_attachment_content_type :source,
    :content_type => ['video/mp4'],
    :message => "Sorry, right now we only support MP4 video",
    :if => :is_type_of_video?
  validates_attachment_content_type :source,
     :content_type => ['image/png', 'image/jpeg', 'image/jpg', 'image/gif'],
     :message => "Different error message",
     :if => :is_type_of_image?
  has_attached_file :source

  protected
  def is_type_of_video?
    source.content_type =~ %r(video)
  end

  def is_type_of_image?
    source.content_type =~ %r(image)
  end

Form fields Validation

 validates_length_of :first_name, maximum: 30
  validates_length_of :last_name, maximum: 30, message: "less than 30 if you don't mind"
  validates_length_of :fax, in: 7..32, allow_nil: true
  validates_length_of :phone, in: 7..32, allow_blank: true
  validates_length_of :user_name, within: 6..20, too_long: 'pick a shorter name', too_short: 'pick a longer name'
  validates_length_of :zip_code, minimum: 5, too_short: 'please enter at least 5 characters'
  validates_length_of :smurf_leader, is: 4, message: "papa is spelled with 4 characters... don't play me."
  validates_length_of :essay, minimum: 100, too_short: 'Your essay must be at least 100 words.',
                      tokenizer: ->(str) { str.scan(/\w+/) }