Improved caching on WP_Site_Query

[spacedmonkey]

In WP_Site_Query, queries are cached as a list of site ids. The key cache is generated using the query args. But even through the values in the cache are the same, if you query by 'fields' => 'all' and 'fields' => 'ids', two caches are generated. By unsetting the 'fields' arg before generating the cache key, both queries will use the same cache.

[flixos90]

41197.diff​ looks good, there are just a few things that can be improved:

• The $fields argument can always be unset, even if $count is true, as that parameter will already distinguish in the cache key between whether to store a count or not.
• For the unit tests, it would be better to have three distinct tests (only one assertion per test):
  • Run the same query twice, once with $fields set to all, the other with $fields set to ids. $wpdb->num_queries should match.
  • Another one similar to the above, but with $count set to true in both queries. $wpdb->num_queries should match.
  • Run the same query twice (with the same $fields value!), but one time with the $count argument as true. $wpdb->num_queries should differ.

[flixos90]

Per discussion with @spacedmonkey, he'll take care of what still needs to happen here.

[spacedmonkey]

@flixos90 feedback completed as requested. Names of the tests might need changing.

[flixos90]

Thanks @spacedmonkey. Will review soon.

[flixos90]

In 41059:

Multisite: Improve caching in WP_Site_Query by ignoring the $fields argument.

Prior to this change there were two different cache keys used for the same query. That is because regardless of the $fields argument, the query response will be the same.

Props spacedmonkey.
Fixes #41197.