Uploading to S3 while model is being created

[lekevicius]

Apologies for using issues as a request for help, but hopefully someone can help me.

In the form, User model is created and avatar is uploaded at the same time. It means that Avatar is uploaded before User is created and has an id. I would like to give a photo UUID (rename from original filename my_photo.jpg to UUID.jpg) and persist that, instead of original file_name, like arc_ecto does by default.

What should I do to rename uploaded file to UUID and persist that to a database (instead of original filename)?

[andreapavoni]

Your question is a bit too generic because you didn't specified if you are trying to store files in dedicated folders and/or you're going to generate several versions of the image.

As a hint, you can do this:

• generate a UUID in changeset and append into a dedicated field in your schema (say uuid), this will be saved within your model. Be sure to do this before calling cast_attachments, otherwise the scope will have uuid set to nil:

def changeset(struct, params \\ %{}) do
  struct
  |> cast(...)
  |> put_change(:uuid, UUID.uuid4())
  |> cast_attachments(...)
  |> ...
end

• override the function filename in your definition file (aka uploader), I suppose you called it Avatar, like in the examples provided in README. Then something like this should work:

def filename(_version, {_file, scope}) do
  "#{scope.uuid}"
end

if you also want different versions, then modify the function like this:

def filename(version, {_file, scope}) do
  "{scope.uuid}_#{version}"
end

hope this helps ;-)

[lekevicius]

Here's the final solution that satisfied me - works without adding additional field to schema, and instead renames uploaded filename and persists that to database:

Person model:

def changeset(struct, params \\ %{}) do
  params = if params["photo"] do
    %{ params | "photo" => %Plug.Upload{ params["photo"] | filename: UUID.uuid4() <> Path.extname(params["photo"].filename) } }
  else
    param
  end

  struct
  |> cast(params, [:first_name, :last_name])
  |> cast_attachments(params, [:photo])
end

Photo uploader:

def filename(version, {file, _scope}) do
  "#{Path.rootname(file.file_name)}_#{version}"
end

Works really well: all versions are saved, useless original filename is not persisted, instead it renames it to UUID and deals with that normally.

[andreapavoni]

Does it work across non-valid forms? It looks like your UUID generation happens every time you call changeset. So in case you have to re-submit the form, you'll get different filenames from the first submit.
Another pain point is the storage_dir: in my use case, I want to namespace each upload (and its versions as well) under a unique/dedicated folder, this can't be done by only renaming filenames.

That's why I've used an additional field on schema.

For completeness, here's how I've implemented filename and storage_dir in my uploader definition:

...
def storage_dir(_, {_file, scope}) do
  "uploads/images/#{scope.uuid}"
end

def filename(_version, {file, _scope}) do
  "#{Path.rootname(file.file_name)}"
end
...

as you can see, I don't care about filenames, but I care to store file(s) under a unique folder.

[andreyk-code]

Believe this is duplicate of #15
There are more example workarounds on that thread

[andreapavoni]

@andreyk-code they're related because that's the same problem, but they don't solve it as well.

btw, I've forked arc_ecto to use a different approach/workaround. it's not perfect, but it's working well in production on 2 apps.

Here's the fork in case you're interested: https://github.com/FunkyStudioHQ/arc_ecto_ng