Changing waffle filename implementation on the fly

Hi, I’m using waffle to upload files a s3 bucket. It’s been working well by I’ve decided I wan’t to change what names are used for the files. So i implement the filename/2 as follows:

  # Override the persisted filenames:
  def filename(version, {file, scope}) do
    file_name = Path.basename(file.file_name, Path.extname(file.file_name))

But now all my already uploaded files have incorrect references to them. Anyone know of a good way to do this, I guess I could just compare the files updated_at timestamp to see if it happend before or after the updated filename definition but I get the feeling I’m missing a more elegant solution.

Thanks in advance, any suggestions are appreciated :slight_smile:

Not sure there’s an elegant solution per se. Maybe you should make a script that retroactively changes the filenames of all files who don’t conform to the new format yet.

You might be interested in this issue on Github: Support dynamic file naming.

Had the same problem recently, you can also make the change of filename by tweaking the changeset (see However, Waffle automatically added file extension and I gave up with this solution. Using the underlying ExAws.S3 is actually not hard and gives more flexibility if you don’t need advanced Waffle features.


Thanks for your suggestions!
After banging my head against this trying to to find a safe and effective solution i decided to solve the problem outside of waffle. So in my controllers I now have a function that goes through the attachments in the parameters and adjusts the filenames in the different %Plug.Upload{}.

  def unique_attachments(params, options \\ []) do
    defaults = [
      field: "attachments"

    options = defaults |> Keyword.merge(options) |> Enum.into(%{})

    attachments = Map.get(params, options.field, %{})

    Enum.reduce(attachments, %{}, fn {key, value}, acc ->
      case Map.get(value, "file", nil) do
        nil ->
          Map.put(acc, key, value)

        file ->
          filename = Map.fetch!(file, :filename)
          unique_filename = "#{:os.system_time()}_#{filename}"
          file = Map.put(file, :filename, unique_filename)
          value = Map.put(value, "file", file)
          Map.put(acc, key, value)

It’s not elegant but it works and it does not risk corrupting my old existing attachments, since it will only apply to new files. :slightly_smiling_face:

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