A blob is a record that contains the metadata about a file and a key for where that file resides on the service. Blobs can be created in two ways:
-
Subsequent to the file being uploaded server-side to the service via
create_after_upload!
. -
Ahead of the file being directly uploaded client-side to the service via
create_before_direct_upload!
.
The first option doesn't require any client-side JavaScript integration, and can be used by any other back-end service that deals with files. The second option is faster, since you're not using your own server as a staging point for uploads, and can work with deployments like Heroku that do not provide large amounts of disk space.
Blobs are intended to be immutable in as-so-far as their reference to a specific file goes. You're allowed to update a blob's metadata on a subsequent pass, but you should not update the key or change the uploaded file. If you need to create a derivative or otherwise change the blob, simply create a new blob and purge the old one.
- MODULE ActiveStorage::Blob::Analyzable
- MODULE ActiveStorage::Blob::Identifiable
- MODULE ActiveStorage::Blob::Representable
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- ActiveStorage::Blob::Analyzable
- ActiveStorage::Blob::Identifiable
- ActiveStorage::Blob::Representable
Returns a new, unsaved blob instance after the io
has been uploaded to the service.
Returns a saved blob instance after the io
has been uploaded to the service. Note, the blob is first built, then the io
is uploaded, then the blob is saved. This is done this way to avoid uploading (which may take time), while having an open database transaction.
Returns a saved blob without uploading a file to the service. This blob will point to a key where there is no file yet. It's intended to be used together with a client-side upload, which will first create the blob in order to produce the signed URL for uploading. This signed URL points to the key generated by the blob. Once the form using the direct upload is submitted, the blob can be associated with the right record using the signed ID.
# File activestorage/app/models/active_storage/blob.rb, line 73 def create_before_direct_upload!(filename:, byte_size:, checksum:, content_type: nil, metadata: nil) create! filename: filename, byte_size: byte_size, checksum: checksum, content_type: content_type, metadata: metadata end
You can used the signed ID of a blob to refer to it on the client side without fear of tampering. This is particularly helpful for direct uploads where the client-side needs to refer to the blob that was created ahead of the upload itself on form submission.
The signed ID is also used to create stable URLs for the blob through the BlobsController.
Returns true if the content_type of this blob is in the audio range, like audio/mpeg.
Deletes the file on the service that's associated with this blob. This should only be done if the blob is going to be deleted as well or you will essentially have a dead reference. It's recommended to use the #purge
and #purge_later
methods in most circumstances.
Downloads the file associated with this blob. If no block is given, the entire file is read into memory and returned. That'll use a lot of RAM for very large files. If a block is given, then the download is streamed and yielded in chunks.
Returns an ActiveStorage::Filename
instance of the filename that can be queried for basename, extension, and a sanitized version of the filename that's safe to use in URLs.
Returns true if the content_type of this blob is in the image range, like image/png.
Returns the key pointing to the file on the service that's associated with this blob. The key is in the standard secure-token format from Rails. So it'll look like: XTAPjJCJiuDrLk3TmwyJGpUo. This key is not intended to be revealed directly to the user. Always refer to blobs using the signed_id
or a verified form of the key.
Deletes the file on the service and then destroys the blob record. This is the recommended way to dispose of unwanted blobs. Note, though, that deleting the file off the service will initiate a HTTP connection to the service, which may be slow or prevented, so you should not use this method inside a transaction or in callbacks. Use #purge_later
instead.
Enqueues an ActiveStorage::PurgeJob
job that'll call purge
. This is the recommended way to purge blobs when the call needs to be made from a transaction, a callback, or any other real-time scenario.
Returns a Hash
of headers for service_url_for_direct_upload
requests.
Returns the URL of the blob on the service. This URL is intended to be short-lived for security and not used directly with users. Instead, the service_url
should only be exposed as a redirect from a stable, possibly authenticated URL. Hiding the service_url
behind a redirect also gives you the power to change services without updating all URLs. And it allows permanent URLs that redirect to the service_url
to be cached in the view.
# File activestorage/app/models/active_storage/blob.rb, line 124 def service_url(expires_in: service.url_expires_in, disposition: :inline, filename: nil, **options) filename = ActiveStorage::Filename.wrap(filename || self.filename) service.url key, expires_in: expires_in, filename: filename, content_type: content_type_for_service_url, disposition: forced_disposition_for_service_url || disposition, **options end
Returns a URL that can be used to directly upload a file for this blob on the service. This URL is intended to be short-lived for security and only generated on-demand by the client-side JavaScript responsible for doing the uploading.
Returns a signed ID for this blob that's suitable for reference on the client-side without fear of tampering. It uses the framework-wide verifier on ActiveStorage.verifier
, but with a dedicated purpose.
Returns true if the content_type of this blob is in the text range, like text/plain.
Uploads the io
to the service on the key
for this blob. Blobs are intended to be immutable, so you shouldn't be using this method after a file has already been uploaded to fit with a blob. If you want to create a derivative blob, you should instead simply create a new blob based on the old one.
Prior to uploading, we compute the checksum, which is sent to the service for transit integrity validation. If the checksum does not match what the service receives, an exception will be raised. We also measure the size of the io
and store that in byte_size
on the blob record.
Normally, you do not have to call this method directly at all. Use the factory class methods of build_after_upload
and create_after_upload!
.
# File activestorage/app/models/active_storage/blob.rb, line 153 def upload(io) self.checksum = compute_checksum_in_chunks(io) self.content_type = extract_content_type(io) self.byte_size = io.size self.identified = true service.upload key, io, checksum: checksum, **service_metadata end