Methods

Instance Public methods

preview(transformations)

Returns an ActiveStorage::Preview instance with the set of transformations provided. A preview is an image generated from a non-image blob. Active Storage comes with built-in previewers for videos and PDF documents. The video previewer extracts the first frame from a video and the PDF previewer extracts the first page from a PDF document.

blob.preview(resize_to_limit: [100, 100]).processed.url

Avoid processing previews synchronously in views. Instead, link to a controller action that processes them on demand. Active Storage provides one, but you may want to create your own (for example, if you need authentication). Here’s how to use the built-in version:

<%= image_tag video.preview(resize_to_limit: [100, 100]) %>

This method raises ActiveStorage::UnpreviewableError if no previewer accepts the receiving blob. To determine whether a blob is accepted by any previewer, call ActiveStorage::Blob#previewable?.

πŸ“ Source code 
# File activestorage/app/models/active_storage/blob/representable.rb, line 63
  def preview(transformations)
    if previewable?
      ActiveStorage::Preview.new(self, transformations)
    else
      raise ActiveStorage::UnpreviewableError, "No previewer found for blob with ID=#{id} and content_type=#{content_type}"
    end
  end
πŸ”Ž See on GitHub

previewable?()

Returns true if any registered previewer accepts the blob. By default, this will return true for videos and PDF documents.

πŸ“ Source code 
# File activestorage/app/models/active_storage/blob/representable.rb, line 72
  def previewable?
    ActiveStorage.previewers.any? { |klass| klass.accept?(self) }
  end
πŸ”Ž See on GitHub

representable?()

Returns true if the blob is variable or previewable.

πŸ“ Source code 
# File activestorage/app/models/active_storage/blob/representable.rb, line 97
  def representable?
    variable? || previewable?
  end
πŸ”Ž See on GitHub

representation(transformations)

Returns an ActiveStorage::Preview for a previewable blob or an ActiveStorage::Variant for a variable image blob.

blob.representation(resize_to_limit: [100, 100]).processed.url

Raises ActiveStorage::UnrepresentableError if the receiving blob is neither variable nor previewable. Call ActiveStorage::Blob#representable? to determine whether a blob is representable.

See ActiveStorage::Blob#preview and ActiveStorage::Blob#variant for more information.

πŸ“ Source code 
# File activestorage/app/models/active_storage/blob/representable.rb, line 85
  def representation(transformations)
    case
    when previewable?
      preview transformations
    when variable?
      variant transformations
    else
      raise ActiveStorage::UnrepresentableError, "No previewer found and can't transform blob with ID=#{id} and content_type=#{content_type}"
    end
  end
πŸ”Ž See on GitHub

variable?()

Returns true if the variant processor can transform the blob (its content type is in ActiveStorage.variable_content_types).

πŸ“ Source code 
# File activestorage/app/models/active_storage/blob/representable.rb, line 44
  def variable?
    ActiveStorage.variable_content_types.include?(content_type)
  end
πŸ”Ž See on GitHub

variant(transformations)

Returns an ActiveStorage::Variant or ActiveStorage::VariantWithRecord instance with the set of transformations provided. This is only relevant for image files, and it allows any image to be transformed for size, colors, and the like. Example:

avatar.variant(resize_to_limit: [100, 100]).processed.url

This will create and process a variant of the avatar blob that’s constrained to a height and width of 100px. Then it’ll upload said variant to the service according to a derivative key of the blob and the transformations.

Frequently, though, you don’t actually want to transform the variant right away. But rather simply refer to a specific variant that can be created by a controller on-demand. Like so:

<%= image_tag Current.user.avatar.variant(resize_to_limit: [100, 100]) %>

This will create a URL for that specific blob with that specific variant, which the ActiveStorage::RepresentationsController can then produce on-demand.

Raises ActiveStorage::InvariableError if the variant processor cannot transform the blob. To determine whether a blob is variable, call ActiveStorage::Blob#variable?.

πŸ“ Source code 
# File activestorage/app/models/active_storage/blob/representable.rb, line 34
  def variant(transformations)
    if variable?
      variant_class.new(self, ActiveStorage::Variation.wrap(transformations).default_to(default_variant_transformations))
    else
      raise ActiveStorage::InvariableError, "Can't transform blob with ID=#{id} and content_type=#{content_type}"
    end
  end
πŸ”Ž See on GitHub