How do I use fields => ids in an array with WP Query?

Question

In my example below, when using fields => ids https://developer.wordpress.org/reference/classes/wp_query/#return-fields-parameter to get an array of post IDs, why does var_dump($args->posts) show NULL when WP_Query($args) does work in my posts loop?

This is an 10 year old question an answer that I'm using as reference Get post ids from WP_Query? and the accepted answer does not work for me.

$one_year_ago = date('F j, Y', strtotime('-364 days'));
$one_year_ago_plus_four = date('F j, Y', strtotime('-369 days'));

$args = array(
      'post_type' => 'post',
      'posts_per_page' => 5,
      'post_status' => 'publish',
      'orderby' => 'date',
      'order' => 'DESC',
      'fields' => 'ids',
      'date_query' => array(
            array(
                'before'    => $one_year_ago,
                'after'     => $one_year_ago_plus_four,
                'inclusive' => true,
            ),
       ),
 );

// Why is $args null?
var_dump($args->posts);
?>

// My post loop works:
<?php $query = new WP_Query($args);
while($query->have_posts()) : $query->the_post(); .....

Edit 10/10/25:

With Ruchita Sojitra's answer, var_dump($query->posts); now shows this:

array(5) { [0]=> int(274354) [1]=> int(274243) [2]=> int(274240) [3]=> int(274225) [4]=> int(274221) }

So that works. But my end goal is to have a string of post IDs as a variable, but using this:

$post_ids_string = implode( ',', $query );
echo $post_ids_string;

throws the error implode(): Argument #2 ($array) must be of type ?array.

Update: Thanks to Philipp Zedler, this works: $post_ids_string = implode( ',', $query->posts );

Because you're passing $query to implode but you'r dumping $query->posts. You need to implode $query->posts. — Jacob Peattie
– Jacob Peattie, Commented Oct 14 at 11:16

Ruchita Sojitra · Accepted Answer · 2025-10-10 06:49:29Z

3

Why is $args null?

$args is just a plain PHP array of query arguments.
Arrays in PHP do not have properties (like $args->posts).
The ->posts property only exists after you instantiate a WP_Query object.
So at that point in your code, $args->posts will always be null or throw an error, because $args is not a WP_Query instance.

Try below the code.

$one_year_ago_start = date('Y-m-d', strtotime('-369 days'));
$one_year_ago_end   = date('Y-m-d', strtotime('-364 days'));
$args = array(
    'post_type'      => 'post',
    'posts_per_page' => 5,
    'post_status'    => 'publish',
    'orderby'        => 'date',
    'order'          => 'DESC',
    'fields'         => 'ids',
    'date_query'     => array(
        array(
            'after'     => $one_year_ago_start,
            'before'    => $one_year_ago_end,
            'inclusive' => true,
        ),
    ),
);
$query = new WP_Query($args);
var_dump($query->posts);
if ($query->have_posts()) :
while ($query->have_posts()) : $query->the_post();
echo get_the_title();
endwhile;
wp_reset_postdata();
endif;

edited Oct 10 at 6:49

answered Oct 10 at 5:34

Ruchita Sojitra

484 bronze badges

Thanks! That works. My mistake. But what I am trying to do is get a string of post IDs, and now I see implode(): Argument #2 ($array) must be of type ?array

BlueDogRanch
– BlueDogRanch

2025-10-10 14:50:20 +00:00
Commented Oct 10 at 14:50
1

Try: $post_ids_string = implode( ',', $query->posts );

Philipp Zedler
– Philipp Zedler

2025-10-10 15:35:34 +00:00
Commented Oct 10 at 15:35
@PhilippZedler Thanks! That worked.

BlueDogRanch
– BlueDogRanch

2025-10-10 17:30:26 +00:00
Commented Oct 10 at 17:30

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