WP_Query() not filtering posts for category

Question

I'm trying to create a custom page for a WordPress theme, which is a child theme of the Twenty Twenty theme. I'm simply trying to use WP_Query() to filter out posts so that it only displays posts with the category slug locations, however it produces two issues.

1.) It does not filter out the posts, and shows posts in any category.

2.) The error Notice:

Undefined offset: 9 in /Users/g/Documents/MAMP/childtheme/wp-includes/class-wp-query.php on line 3271 repeats over and over with increasing offsets numbers until the browser crashes.

$q = new WP_Query( array('category_name' => 'locations' ));

if ( $q->have_posts() ) {

    while ( $q->have_posts() ) {

        the_post();
        get_template_part( 'template-parts/content', get_post_type() );

    }
} 

I have a feeling it's something silly, but I have been at it for a few hours and haven't found the issue. Any help would be appreciated.

Answer 1

the_post() operates on the main query, but this isn't the main query you're looping over, you need to use $q->the_post()

Remember:

• the_post() is the same as global $wp_query; $wp_query->the_post();
• All post loops are WP_Query post loops if you dig down deep enough, even get_posts has a WP_Query inside it
• There can only be 1 current post in $post, calling the_post sets that global variable.

This is what a standard post loop should look like:

$args = [
    // parameters go here
];
$query = new WP_Query( $args );
if ( $query->have_posts() ) { 
    while ( $query->have_posts() ) {
        $query->the_post();
        // display the post
        the_title();
        the_content();
    }
    wp_reset_postdata();
} else {
    esc_html_e( 'no posts were found', 'textdomain' );
}