Resources

Here's our example Resizable Image Validator that validates image content types that are uploaded. We can make sure we only accept image types that are resizable using this validator.

# app/validators/resizable_image_validator.rb
class ResizableImageValidator < ActiveModel::EachValidator
  # Only allow resizable image formats
  # SVGs aren't allowed because they can contain XSS
  #
  def validate_each(record, attribute, value)
    return unless value.attached?

    if ActiveStorage.variable_content_types.exclude?(value.content_type)
      record.errors.add(attribute, :image_format_not_supported)
    end
  end
end

# app/models/user.rb
class User < ApplicationRecord
  has_one_attached :avatar
  validates :avatar, resizable_image: true
end