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: "100x100").processed.service_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: "100x100") %>
This method raises ActiveStorage::UnpreviewableError if no previewer accepts the receiving blob. To determine whether a blob is accepted by any previewer, call #previewable?.
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.
Returns an ActiveStorage::Preview for a previewable blob or an ActiveStorage::Variant for a variable image blob.
blob.representation(resize: "100x100").processed.service_url
Raises ActiveStorage::UnrepresentableError if the receiving blob is neither variable nor previewable. Call #representable? to determine whether a blob is representable.
Returns true if ImageMagick can transform the blob (its content type is in
ActiveStorage.variable_content_types
).
Returns an ActiveStorage::Variant 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: "100x100").processed.service_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: "100x100") %>
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 ImageMagick cannot transform the blob. To determine whether a blob is variable, call #variable?.