[FIXED] Wordpress ajax filter posts by combining multiple taxonomies

Issue

I am working on a filter for a post grid in Wordpress with ajax.

It's fundamentally working as a whole, but I'm trying to filter using multiple taxonomies. But instead of it combining the taxonomies to refine the search such as posts tagged with 'a' AND 'b'

It's just showing all posts with the tag 'a' and with the tag 'b'

$args = array(
    'post_type' => 'projects',
    'orderby' => 'date', // we will sort posts by date
    'order' => $_POST['date'] // ASC or DESC
);

if( isset($_POST['multi_subject']) && !empty($_POST['multi_subject']) ) {
    $args['tax_query'] = array(
        array(
            'taxonomy' => 'category',
            'field' => 'id',
            'terms' => $_POST['multi_subject']
        )
    );
}

if( isset($_POST['multi_style']) && !empty($_POST['multi_style']) ) {
    $args['tax_query'] = array(
        array(
            'taxonomy' => 'styles',
            'field' => 'id',
            'terms' => $_POST['multi_style']
        )
    );
}

$query = new WP_Query( $args );

if( $query->have_posts() ) :
    while( $query->have_posts() ): $query->the_post();

        echo '<a href="'. get_permalink() .'" data-author="'. get_the_author() .'" data-tier="'. get_author_role() .'">';
        echo '<h2>' . $query->post->post_title . '</h2>';
        echo '<div>'. the_post_thumbnail() .'</div>';
        echo '</a>';
    endwhile;
    wp_reset_postdata();
else :
    echo 'No posts found';
endif;

die();

I'm sure it's something simple to do with the isset then setting the args but I can't figure it out.

Solution

Your current tax query does not allow for both taxonomies to be checked cause if both are set your second tax check will overrite the first. To allow for both you need to append them... refactor your tax_query to something like this:

// start with an empty array
$args['tax_query'] = array();

// check for first taxonomy
if( isset($_POST['multi_subject']) && !empty($_POST['multi_subject']) ) {
    // append to the tax array
    $args['tax_query'][] = array(
        'taxonomy' => 'category',
        'field' => 'id',
        'terms' => $_POST['multi_subject']
    );
}

// check for another taxonomy
if( isset($_POST['multi_style']) && !empty($_POST['multi_style']) ) {
    // append to the tax array
    $args['tax_query'][] = array(
        'taxonomy' => 'styles',
        'field' => 'id',
        'terms' => $_POST['multi_style']
    );
}

Answered By - mikerojas