Query multiple taxonomies with pre get posts

Question

I am trying to query a custom post type based on what a user inputs into a form, I am having trouble querying multiple taxonomies in pre_get_posts filter, I can't seem to find a way to set the query more than one taxonomy

function custom_search( $query ) {
if ( is_archive('experts') && $query->is_main_query() && !is_admin() ) {

    $keyword = get_query_var( 'keyword', FALSE );
    $industry_select = strtolower(str_replace(' ', '-', get_query_var( 'industry_select', FALSE ) ));
    $speciality_select = strtolower(str_replace(' ', '-', get_query_var( 'speciality', FALSE ) ));
  
    // Keywords query
    $keyword ? $keyword : $keyword = null;

    $query->set('s', $keyword);
    
    // Taxonomies query

    $tax_query_array = array('relation' => 'OR');
    $speciality_select ? array_push($tax_query_array, array('taxonomy' => 'experts_specialities', 'field' => 'slug', 'terms' => $speciality_select) ) : null ;
    $query->set( 'tax_query', $tax_query_array);

    $tax_query_array = array('relation' => 'OR');
    $industry_select ? array_push($tax_query_array, array('taxonomy' => 'experts_industries', 'field' => 'slug', 'terms' => $industry_select) ) : null ;
    $query->set( 'tax_query', $tax_query_array);
}}
add_action( 'pre_get_posts', 'custom_search' );

In the past I have written queries that look like the following that successfully look in two taxonomies (eventually I need to have 3 taxonomies though)

$featured_args = array(
    'post_type'  => 'experts',
    'hide_empty' => false ,
    'paged'      => $paged,
    'tax_query' => array(
        array(
            'taxonomy' => 'experts_industries',
            'field' => 'slug',
            'terms' => $broad_match_ind
        ),
        array(
            'taxonomy' => 'experts_specialities',
            'field' => 'slug',
            'terms' => $broad_match_spec
        )
    )
);

I'm trying to use pre_get_posts because I ultimately want the results of this query on an archive page and don't want to create a second query with a set of args ( as I am currently doing as evidenced by my second code example above )

Thanks in advance.

Answer 1

I can't seem to find a way to set the query more than one taxonomy

You already found it, but the problem is, you should have not done this:

$tax_query_array = array('relation' => 'OR');
$speciality_select ? array_push($tax_query_array, ...) : null ;
$query->set( 'tax_query', $tax_query_array);

$tax_query_array = array('relation' => 'OR');
$industry_select ? array_push($tax_query_array, ...) : null ;
$query->set( 'tax_query', $tax_query_array);

.. because the 2nd $query->set() call overrides the entire tax_query array that's set via the 1st $query->set() call.

And to fix the issue, just remove the 1st $query->set() call and the 2nd $tax_query_array = array('relation' => 'OR');, i.e. lines 3 and 5 above.

Also, keep in mind that is_archive() does not accept any parameters. So if you wanted to check if the query is for a specific post type archive, use is_post_type_archive() instead, i.e. is_post_type_archive( 'experts' ).

And.. I don't think the $keyword ? $keyword : $keyword = null; is necessary, so I'd just remove that and simply do $query->set('s', $keyword);.