Best way to add metadata to a derivative when generating?

[jrochkind]

I realized I want to store my derivatives with some custom per-derivative metadata. Since derivatives are just shrine uploaded files and go through an uploader, they DO have metadata stored with them, just whatever metadata was created by the uploader.

But I have some things that are artifacts of the creation process that I want to explicitly specify at the same time I'm specifying the binary data fro the derivative. Say, the version number of an external dependency used to create the derivative.

What are the various ways or the best way I could specify metadata when saving a derivative?

I'm currently using the Attacher.derivatives method, like the example from docs:

  Attacher.derivatives :thumbnails do |original|
    { large: ..., medium: ..., small: ... }
  end

But in that API you provide a hash of keys and binary data, no way to add metadata?

I thought of doing something complex involving storing metadata to add temporarily in the shrine context, and then having a custom uploader with over-ridden extract_metadata that finds the metadata stored in context and adds it only if it's being called on a derivative... which seems like it could work, but is there a better way?

Thanks for any ideas!

[janko]

Sorry for the late reply. The most high-level method for generating derivatives Attacher#create_derivatives, which internally calls Attacher#process_derivatives (this calls your Attacher.derivatives block) and then calls Attacher#add_derivatives.

The Attacher#create_derivatives method doesn't support passing metadata, but Attacher#add_derivatives should accept the metadata: keyword argument. So, if you just call these two methods separately, you should be good to go.

If you need per-derivative metadata, then I recommend not using an Attacher.derivatives block but just generating derivatives manually.

[jrochkind]

thanks!