$query->post is null when WP_Query `fields` parameter is present

[wujek_bogdan]

Normally, WP_Query returns an object where $query->posts contains an array of posts and $query->post contains the first post. But if the fields parameter is present then $query->post returns null. Is it a bug or an expected behaviour? If it's expected then it should be documented because it's confusing and unintuitive.

Example:

<?php

// Works as expected
$query = new \WP_Query([
    'post_type' => 'my-post-type',
]);

if ($query->have_posts()) {
    $firstPost = $query->post; // returns the same as $query->$posts[0]
}

// Weird behaviour
$query = new \WP_Query([
    'post_type' => 'my-post-type',
    'fields'    => 'ids',
]);

if ($query->have_posts()) {
    $firstPost = $query->post; // returns null
}

[mukesh27]

@wujek_bogdan i have checked above issue and found that it's bug in core software. When any WP_Query use fields argument with ids or id=>parent option then system does not set it post variable for that query result and system show null value in result.

[mukesh27]

Patch

[callumbw95]

Modernised patch as the previous patch wasn't working in the latest version of WordPress

[callumbw95]

Hi all,
I know this is an older issue now but as its still occurring in the latest release and on trunk I thought I would throw my hat in to the ring to get this resolved. I have taken a look at the previous patch, and this didn't appear to work in the current version. Because of this I have updated the patch and tested this and all appears to be working now. Hopefully this can help unstick this ticket.

[callumbw95]

Hi again, I should have done a bit more digging before submitting my patch, as it seems between this ticket initially being raised and now the $query->post variable is now documented as being set to null when passing 'ids' or 'id=>parent' to the fields argument. As of such this ticket most likely should be closed as it is no longer relevant in the latest version of WordPress.

[mindctrl]

Hi all, as Callum mentioned above, this is now documented as expected behavior. Source: ​https://github.com/WordPress/wordpress-develop/blob/6d26f584fb3b9d97d5a07084aef0a707c7b42b70/src/wp-includes/class-wp-query.php#L127-L136

With that in mind, I'm going to close this ticket to help clean up Trac. Feel free to reopen if you think the intended behavior should change.