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module ActiveStorage::Blob::Representable

Public instance 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?.

Source code GitHub 
# File activestorage/app/models/active_storage/blob/representable.rb, line 129
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

previewable?()

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

Source code GitHub 
# File activestorage/app/models/active_storage/blob/representable.rb, line 138
def previewable?
  ActiveStorage.previewers.any? { |klass| klass.accept?(self) }
end

representable?()

Returns true if the blob is variable or previewable.

Source code GitHub 
# File activestorage/app/models/active_storage/blob/representable.rb, line 163
def representable?
  variable? || previewable?
end

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.

Source code GitHub 
# File activestorage/app/models/active_storage/blob/representable.rb, line 151
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

variable?()

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

Source code GitHub 
# File activestorage/app/models/active_storage/blob/representable.rb, line 110
def variable?
  ActiveStorage.variable_content_types.include?(content_type)
end

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?.

Options

Options are defined by the image_processing gem, and depend on which variant processor you are using: Vips or MiniMagick. However, both variant processors support the following options:

:resize_to_limit

Downsizes the image to fit within the specified dimensions while retaining the original aspect ratio. Will only resize the image if it’s larger than the specified dimensions.

user.avatar.variant(resize_to_limit: [100, 100])
:resize_to_fit

Resizes the image to fit within the specified dimensions while retaining the original aspect ratio. Will downsize the image if it’s larger than the specified dimensions or upsize if it’s smaller.

user.avatar.variant(resize_to_fit: [100, 100])
:resize_to_fill

Resizes the image to fill the specified dimensions while retaining the original aspect ratio. If necessary, will crop the image in the larger dimension.

user.avatar.variant(resize_to_fill: [100, 100])
:resize_and_pad

Resizes the image to fit within the specified dimensions while retaining the original aspect ratio. If necessary, will pad the remaining area with transparent color if source image has alpha channel, black otherwise.

user.avatar.variant(resize_and_pad: [100, 100])
:crop

Extracts an area from an image. The first two arguments are the left and top edges of area to extract, while the last two arguments are the width and height of the area to extract.

user.avatar.variant(crop: [20, 50, 300, 300])
:rotate

Rotates the image by the specified angle.

user.avatar.variant(rotate: 90)

Some options, including those listed above, can accept additional processor-specific values which can be passed as a trailing hash:

<!-- Vips supports configuring `crop` for many of its transformations -->
<%= image_tag user.avatar.variant(resize_to_fill: [100, 100, { crop: :centre }]) %>

If migrating an existing application between MiniMagick and Vips, you will need to update processor-specific options:

<!-- MiniMagick -->
<%= image_tag user.avatar.variant(resize_to_limit: [100, 100], format: :jpeg,
      sampling_factor: "4:2:0", strip: true, interlace: "JPEG", colorspace: "sRGB", quality: 80) %>

<!-- Vips -->
<%= image_tag user.avatar.variant(resize_to_limit: [100, 100], format: :jpeg,
      saver: { subsample_mode: "on", strip: true, interlace: true, quality: 80 }) %>
Source code GitHub 
# File activestorage/app/models/active_storage/blob/representable.rb, line 100
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

Definition files