Alright, the controllers are migrated, but still needs unit tests converted across. (I suspect I'll find further bugs as those are migrated.)

I was hoping to include a _link in the Posts response to the meta endpoint, but cannot seem to find the appropriate relationship: http://www.iana.org/assignments/link-relations/link-relations.xhtml#link-relations-1

I am going to be out for the next 2-3 days, and haven't found a great approach for the remaining open items here. @rmccue or @joehoyle welcome to pick this up, if you can

Meta schema & schema route

Done.

Meta links in endpoint responses
Links to the meta routes in Posts responses

Not sure what the difference between these is? I've added the link from the post out to the meta items, was the other just the reverse of that?

This is no longer [WIP] and is up for review.

One note: @danielbachhuber said above:

Rather than subclassing, let's pass $type to WP_JSON_Meta_Controller, similar to WP_JSON_Posts_Controller

Unlike the posts controller, we have two fundamentally different objects (posts and users, with potentially comments and terms) that have different permissions checks and such. For example, comment meta would need to check the comment and potentially also the parent post.

@WP-API/amigos #reviewmerge

Unlike the posts controller, we have two fundamentally different objects (posts and users, with potentially comments and terms) that have different permissions checks and such.

Couldn't we have some conditional logic based on $type inside of the permissions callback?

Pages are fundamentally different than Posts, and we've accommodated them both just fine in the Posts controller.

@joehoyle thoughts?

Couldn't we have some conditional logic based on $type inside of the permissions callback?

We have a small amount right now, yeah (get_id_column), but I'm tempted to even move that to the subclasses.

Pages and posts are both fundamentally CPTs, so they follow a bunch of similar patterns. Both store meta in the database equally, both have the same system to check permissions, etc. Posts and users however are a fair bit different.

We could do it, but we'll end up with some kinda nasty conditionals in the permission checks. As is, the permission checks are essentially the only place we need to subclass right now, so I think it's fine as-is. We can always revisit and refactor if we need to when we add user meta.