[wp-trac] [WordPress Trac] #44387: Add support for site meta in `register_meta()`

[WordPress Trac]

#44387: Add support for site meta in `register_meta()`
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 Reporter:  flixos90            |      Owner:  (none)
     Type:  enhancement         |     Status:  new
 Priority:  normal              |  Milestone:  5.0
Component:  Options, Meta APIs  |    Version:
 Severity:  normal              |   Keywords:  2nd-opinion
  Focuses:  multisite           |
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 #38323 adds subtype handling to `register_meta()`. These efforts include
 introducing a function `get_object_subtype()` which returns the object
 subtype of a given type and ID combination. For the initial merge, this
 only includes the single site types "post", "term", "comment" and "user".
 Since [42836], sites in a multisite also support metadata, so they should
 receive subtype support as well.

 Since sites do not actually use subtypes at this point, we basically only
 need to add a clause which checks whether a site with the given ID exists,
 and if so, return the type identifier.

 The tricky part into which we need to put some thought is the naming:
 Sites have been historically called "blogs", and WordPress core aims to
 get rid of the legacy naming in its APIs (and only the database schema
 remains untouched). For example, there are wrapper functions like
 `get_site_meta()`, but they actually call the low-level meta functions
 like `get_metadata( 'blog', ... )` because those are tightly coupled to
 the DB schema. Since registering site meta would be new, we should
 consider actually naming the type "site" here, and then only internally
 handling the "blog" part of it. However, this may introduce unexpected
 inconsistencies with other areas, so we need to investigate whether this
 is a wise choice or not.

 I'd generally argue the simplest solution would be to introduce
 `register_site_meta()` and `unregister_site_meta()` and otherwise keep the
 "blog" name (which would be consistent with the way existing site meta
 wrappers work) - however we decided wrappers should only be introduced for
 object types that use subtypes, so here with sites, developers would
 actually need to call `register_meta( 'blog', ... )` themselves which
 would be sub-optimal. Let's discuss.

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Ticket URL: <https://core.trac.wordpress.org/ticket/44387>
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