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:

  1. Subsequent to the file being uploaded server-side to the service via create_after_upload!.

  2. 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.

Namespace

Module

Methods

Included Modules

Class Public methods

build_after_upload(io:, filename:, content_type: nil, metadata: nil)

Returns a new, unsaved blob instance after the io has been uploaded to the service.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 51
    def build_after_upload(io:, filename:, content_type: nil, metadata: nil)
      new.tap do |blob|
        blob.filename     = filename
        blob.content_type = content_type
        blob.metadata     = metadata

        blob.upload io
      end
    end
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create_after_upload!(io:, filename:, content_type: nil, metadata: nil)

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 64
    def create_after_upload!(io:, filename:, content_type: nil, metadata: nil)
      build_after_upload(io: io, filename: filename, content_type: content_type, metadata: metadata).tap(&:save!)
    end
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create_before_direct_upload!(filename:, byte_size:, checksum:, content_type: nil, metadata: nil)

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.

📝 Source code 
# 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
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find_signed(id)

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 46
    def find_signed(id)
      find ActiveStorage.verifier.verify(id, purpose: :blob_id)
    end
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Instance Public methods

audio?()

Returns true if the content_type of this blob is in the audio range, like audio/mpeg.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 105
  def audio?
    content_type.start_with?("audio")
  end
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delete()

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 172
  def delete
    service.delete(key)
    service.delete_prefixed("variants/#{key}/") if image?
  end
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download(&block)

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 164
  def download(&block)
    service.download key, &block
  end
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filename()

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 95
  def filename
    ActiveStorage::Filename.new(self[:filename])
  end
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image?()

Returns true if the content_type of this blob is in the image range, like image/png.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 100
  def image?
    content_type.start_with?("image")
  end
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key()

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 87
  def key
    # We can't wait until the record is first saved to have a key for it
    self[:key] ||= self.class.generate_unique_secure_token
  end
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purge()

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 180
  def purge
    destroy
    delete
  rescue ActiveRecord::InvalidForeignKey
  end
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purge_later()

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 188
  def purge_later
    ActiveStorage::PurgeJob.perform_later(self)
  end
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service_headers_for_direct_upload()

Returns a Hash of headers for service_url_for_direct_upload requests.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 138
  def service_headers_for_direct_upload
    service.headers_for_direct_upload key, filename: filename, content_type: content_type, content_length: byte_size, checksum: checksum
  end
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service_url(expires_in: service.url_expires_in, disposition: :inline, filename: nil, **options)

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.

📝 Source code 
# 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
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service_url_for_direct_upload(expires_in: service.url_expires_in)

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 133
  def service_url_for_direct_upload(expires_in: service.url_expires_in)
    service.url_for_direct_upload key, expires_in: expires_in, content_type: content_type, content_length: byte_size, checksum: checksum
  end
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signed_id()

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.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 80
  def signed_id
    ActiveStorage.verifier.generate(id, purpose: :blob_id)
  end
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text?()

Returns true if the content_type of this blob is in the text range, like text/plain.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 115
  def text?
    content_type.start_with?("text")
  end
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upload(io)

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!.

📝 Source code 
# 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
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video?()

Returns true if the content_type of this blob is in the video range, like video/mp4.

📝 Source code 
# File activestorage/app/models/active_storage/blob.rb, line 110
  def video?
    content_type.start_with?("video")
  end
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