Woocommerce: filter by attribute

Question

I'm currently working on woocommerce, to make an specific request before displaying products. I'm using for that the hook woocommerce_product_query that is executed before the request is done in the class WC_Query in product_query method.

I can access the variable $q (query object), example bellow:

Now I would like to know how to filter this request by some custom attributes. I thought that would be something like that, but nothing is working maybe you could explain why.

add_action( 'woocommerce_product_query', 'filter_products_by_brand' );

function filter_products_by_brand( WP_Query $q ) {

    $tax_query = (array) $q->get( 'tax_query' );


    $tax_query[] = array(
        'taxonomy' => 'cb-brand',
        'field' => 'slug',
        'terms' => array( 'jeep' ),
        'operator' => 'IN'
     );

    $q->set( 'tax_query', $tax_query );
}

WP_Query Object
(
    [query] => Array
        (
            [product_cat] => accessoires-2/attelages/faisceaux
        )

    [query_vars] => Array
        (
            [product_cat] => faisceaux
            [error] => 
            [m] => 
            [p] => 0
            [post_parent] => 
            [subpost] => 
            [subpost_id] => 
            [attachment] => 
            [attachment_id] => 0
            [name] => 
            [pagename] => 
            [page_id] => 0
            [second] => 
            [minute] => 
            [hour] => 
            [day] => 0
            [monthnum] => 0
            [year] => 0
            [w] => 0
            [category_name] => 
            [tag] => 
            [cat] => 
            [tag_id] => 
            [author] => 
            [author_name] => 
            [feed] => 
            [tb] => 
            [paged] => 0
            [meta_key] => 
            [meta_value] => 
            [preview] => 
            [s] => 
            [sentence] => 
            [title] => 
            [fields] => 
            [menu_order] => 
            [embed] => 
            [category__in] => Array
                (
                )

            [category__not_in] => Array
                (
                )

            [category__and] => Array
                (
                )

            [post__in] => Array
                (
                )

            [post__not_in] => Array
                (
                )

            [post_name__in] => Array
                (
                )

            [tag__in] => Array
                (
                )

            [tag__not_in] => Array
                (
                )

            [tag__and] => Array
                (
                )

            [tag_slug__in] => Array
                (
                )

            [tag_slug__and] => Array
                (
                )

            [post_parent__in] => Array
                (
                )

            [post_parent__not_in] => Array
                (
                )

            [author__in] => Array
                (
                )

            [author__not_in] => Array
                (
                )

            [orderby] => menu_order title
            [order] => ASC
            [meta_query] => Array
                (
                )

            [tax_query] => Array
                (
                    [relation] => AND
                    [0] => Array
                        (
                            [taxonomy] => product_visibility
                            [field] => term_taxonomy_id
                            [terms] => Array
                                (
                                    [0] => 7
                                )

                            [operator] => NOT IN
                        )

                )

            [wc_query] => product_query
            [posts_per_page] => 16
        )

    [tax_query] => WP_Tax_Query Object
        (
            [queries] => Array
                (
                    [0] => Array
                        (
                            [taxonomy] => product_cat
                            [terms] => Array
                                (
                                    [0] => faisceaux
                                )

                            [field] => slug
                            [operator] => IN
                            [include_children] => 1
                        )

                )

            [relation] => AND
            [table_aliases:protected] => Array
                (
                )

            [queried_terms] => Array
                (
                    [product_cat] => Array
                        (
                            [terms] => Array
                                (
                                    [0] => faisceaux
                                )

                            [field] => slug
                        )

                )

            [primary_table] => 
            [primary_id_column] => 
        )

    [meta_query] => 
    [date_query] => 
    [queried_object] => WP_Term Object
        (
            [term_id] => 108
            [name] => Faisceaux
            [slug] => faisceaux
            [term_group] => 0
            [term_taxonomy_id] => 108
            [taxonomy] => product_cat
            [description] => 
            [parent] => 106
            [count] => 1
            [filter] => raw
        )

    [queried_object_id] => 108
    [post_count] => 0
    [current_post] => -1
    [in_the_loop] => 
    [comment_count] => 0
    [current_comment] => -1
    [found_posts] => 0
    [max_num_pages] => 0
    [max_num_comment_pages] => 0
    [is_single] => 
    [is_preview] => 
    [is_page] => 
    [is_archive] => 1
    [is_date] => 
    [is_year] => 
    [is_month] => 
    [is_day] => 
    [is_time] => 
    [is_author] => 
    [is_category] => 
    [is_tag] => 
    [is_tax] => 1
    [is_search] => 
    [is_feed] => 
    [is_comment_feed] => 
    [is_trackback] => 
    [is_home] => 
    [is_privacy_policy] => 
    [is_404] => 
    [is_embed] => 
    [is_paged] => 
    [is_admin] => 
    [is_attachment] => 
    [is_singular] => 
    [is_robots] => 
    [is_favicon] => 
    [is_posts_page] => 
    [is_post_type_archive] => 
    [query_vars_hash:WP_Query:private] => a80e55b982d04f2e0de36fdd19a948d6
    [query_vars_changed:WP_Query:private] => 
    [thumbnails_cached] => 
    [stopwords:WP_Query:private] => 
    [compat_fields:WP_Query:private] => Array
        (
            [0] => query_vars_hash
            [1] => query_vars_changed
        )

    [compat_methods:WP_Query:private] => Array
        (
            [0] => init_query_flags
            [1] => parse_tax_query
        )

)

Thanks.

Answer 1

If anyone wants to know.

To make an filter based on an attributes :

add_filter('woocommerce_product_query_tax_query', 'custom_product_query_meta_query', 10, 2);

function custom_product_query_meta_query( $tax_query, $query ) {

     $taxonomy = 'pa_${NAME OF THE ATTRIBUTE}'; // Note: always start with "pa_" in Woocommerce

    $tax_query[] = array(
        'taxonomy'         => $taxonomy,
        'field'            => 'name', // name or slug
        'terms'            =>  array( '1S026015002003' ),
        'operator'         => 'IN',
    );

    return $tax_query;
}