`WP_Comment_Query::fill_descendants()` queries for a comment tree in a way that
minimizes database overhead, and places the located descendants with their
proper parents. However, it doesn't touch leaf nodes - comments with no
children - so future calls to `get_children()` on those comment objects
result in unnecessary database queries. To prevent this, `fill_descendants()`
now sets a `populated_children` flag on all located `WP_Comment` objects.
See #8071.
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[34583] modified comment queries so that all post fields are no longer loaded
by default. Instead, they are loaded only when requested on individual comment
objects. This changeset improves that flow:
* `WP_Comment` magic methods `__isset()` and `__get()` should only load the post when a post field is being requested.
* The new `update_comment_post_cache` argument for `WP_Comment_Query` allows developers to specify that, when comments are queried, all of the posts matching those comments should be loaded into cache with a single DB hit. This parameter defaults to false, since typical comment queries are linked to a single post.
Fixes#27571.
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Previously, the 'page_comments' toggle allowed users to disable comment
pagination. This toggle was only superficial, however. Even with
'page_comments' turned on, `comments_template()` loaded all of a post's
comments into memory, and passed them to `wp_list_comments()` and
`Walker_Comment`, the latter of which produced markup for only the
current page of comments. In other words, it was possible to enable
'page_comments', thereby showing only a subset of a post's comments on a given
page, but all comments continued to be loaded in the background. This technique
scaled poorly. Posts with hundreds or thousands of comments would load slowly,
or not at all, even when the 'comments_per_page' setting was set to a
reasonable number.
Recent changesets have addressed this problem through more efficient tree-
walking, better descendant caching, and more selective queries for top-level
post comments. The current changeset completes the project by addressing the
root issue: that loading a post causes all of its comments to be loaded too.
Here's the breakdown:
* Comment pagination is now forced. Setting 'page_comments' to false leads to evil things when you have many comments. If you want to avoid pagination, set 'comments_per_page' to something high.
* The 'page_comments' setting has been expunged from options-discussion.php, and from places in the codebase where it was referenced. For plugins relying on 'page_comments', we now force the value to `true` with a `pre_option` filter.
* `comments_template()` now queries for an appropriately small number of comments. Usually, this means the `comments_per_page` value.
* To preserve the current (odd) behavior for comment pagination links, some unholy hacks have been inserted into `comments_template()`. The ugliness is insulated in this function for backward compatibility and to minimize collateral damage. A side-effect is that, for certain settings of 'default_comments_page', up to 2x the value of `comments_per_page` might be fetched at a time.
* In support of these changes, a `$format` parameter has been added to `WP_Comment::get_children()`. This param allows you to request a flattened array of comment children, suitable for feeding into `Walker_Comment`.
* `WP_Query` loops are now informed about total available comment counts and comment pages by the `WP_Comment_Query` (`found_comments`, `max_num_pages`), instead of by `Walker_Comment`.
Aside from radical performance improvements in the case of a post with many
comments, this changeset fixes a bug that caused the first page of comments to
be partial (`found_comments` % `comments_per_page`), rather than the last, as
you'd expect.
Props boonebgorges, wonderboymusic.
Fixes#8071.
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Comments can be threaded. Now your query can be threaded too! Bonus: it's
not totally insane.
* The new `$hierarchical` parameter for `WP_Comment_Query` accepts three values:
* `false` - Default value, and equivalent to current behavior. No descendants are fetched for matched comments.
* `'flat'` - `WP_Comment_Query` will fetch the descendant tree for each comment matched by the query paramaters, and append them to the flat array of comments returned. Use this when you have a separate routine for constructing the tree - for example, when passing a list of comments to a `Walker` object.
* `'threaded'` - `WP_Comment_Query` will fetch the descendant tree for each comment, and return it in a tree structure located in the `children` property of the `WP_Comment` objects.
* `WP_Comment` now has a few utility methods for fetching the descendant tree (`get_children()`), fetching a single direct descendant comment (`get_child()`), and adding anothing `WP_Comment` object as a direct descendant (`add_child()`). Note that `add_child()` only modifies the comment object - it does not touch the database.
Props boonebgorges, wonderboymusic.
See #8071.
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* Takes inspiration from `WP_Post` and adds sanity to comment caching.
* Clarifies when the current global value for `$comment` is returned. The current implementation in `get_comment()` introduces side effects and an occasion stale global value for `$comment` when comment caches are cleaned.
* Strongly-types `@param` docs
* This class is marked `final` for now
Props wonderboymusic, nacin.
See #32619.
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Boone Gorges
Scott Taylor
Drew Jaynes