Instance Public methods
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
Returns true if any registered previewer accepts the blob. By default, this will return true for videos and PDF documents.
Returns true if the blob is variable or previewable.
ActiveStorage::Preview for a previewable blob or an
ActiveStorage::Variant for a variable image blob.
blob.representation(resize_to_limit: [100, 100]).processed.url
ActiveStorage::UnrepresentableError if the receiving blob is neither variable nor previewable. Call
ActiveStorage::Blob#representable? to determine whether a blob is representable.
ActiveStorage::Blob#variant for more information.
Returns true if the variant processor can transform the blob (its content type is in
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.
ActiveStorage::InvariableError if the variant processor cannot transform the blob. To determine whether a blob is variable, call
# 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 end end