ActivityPub Query: Improve third party plugin support

[pfefferle]

• Add filter to change the queried object
• Always call transformer

See #1263

[Menrath]

Either this or we could also introduce a query like ?t=<term_id> for ActivityPub requests. This would kind of unify behaviour for third party plugins and maybe reduce the possibility of errors.

But the approach here is indeed useful for some cases: I have already real life examples in mind:

Some event plugins have "events" and "event occurances". Usually the occurances are stored in a custom table, because the posts table is just not adequate for such special cases. This is also what "The Events Calendar" and "GatherPress" do.

With that filter one could easily set an "occurance" as the targeted query, which would not be possible (in an easy and straight-forward way) without the filter I would guess.

Edit: Maybe that example is not good, because the custom transformer might be able to negotiate that, if the related WP_Post object gets "identified" as the queried object by WordPress.

[obenland]

What would be a good way for me to test this change? Go to an author archive page?

[pfefferle]

this handles the content negotiation for authors, posts, comments and all other post-types. so you can check this by calling one or all of these sites with the application/json+activity Accept header.

[pfefferle]

Ah and adding the query bar was only to get sure that we have access to it!