Custom query at top of archive search page, arguments are overridden

Question

I am using a customised archive template for a custom post type.

At the top of the page, I'd like to show a specific post, found using a new wp_query() call.

$args = [
    'posts_per_page' => 1,
    'post_type' => 'document',
    'order' => 'DESC',
    'orderby' => 'date',
];
$query = new WP_Query( $args );
if ( $query->have_posts() ) {
    while ( $query->have_posts() ) {
        $query->the_post();
        the_title();
        the_date( 'F Y' );
    }
    wp_reset_postdata();
}

Custom search form

<form id="document-filter" method="post">
    <select name="order_by">
        <option value="date">Date</option>
        <option value="title">Name</option>
    </select>
    <select name="order">
        <option value="desc">DESC</option>
        <option value="asc">ASC</option>
    </select>
    <input name="s" type="text" placeholder="Filter by keyword" value=""/>
    <input name="post_type" type="hidden" value="document"/>
    <input type="submit" />
</form>

Initially, it works. However, if I then use the custom search form to either sort the archive list (date/name, asc/desc), the custom wp_query() is affected, and the query_vars array is overriding my supplied arguments.

Example

Posts, in date order, descending:

1. Post C
2. Post B
3. Post A

Initially, my custom query at the top of the page will output Post C, which is correct.

If I use the search/filter form to change the order of the posts to:

1. Post A
2. Post B
3. Post C

The singular queried post will now be Post A, which is incorrect. My custom query args have not changed, but are being overridden by the search form somehow.

Answer 1

In my experience wp_reset_postdata() does not work well. You can try this code:

global $wp_query;
$temp_wp_query = $wp_query;
//Your custom WP_Query code
$wp_query = $temp_wp_query;

Answer 2

So I finally got this working, but not using wp_query().

Instead, I had to use a custom query with $wpdb.

Example:

$latest_document = $wpdb->get_results( $wpdb->prepare( "
        SELECT $wpdb->posts.*
        FROM $wpdb->posts
        WHERE $wpdb->posts.post_status = %s
        AND $wpdb->posts.post_type = %s
        ORDER BY $wpdb->posts.post_date DESC
        LIMIT 1
     ", 'publish', 'document' ), OBJECT );

What is interesting is that whilst I am only wanting a single row, when I used $wpdb->get_row() I got the same issue as before, where the resulting record would be sorted by the parameters from the search form.

Using $wpdb->get_results() works fine and the record is consistently the same, regardless of the sorting I select using the search form.