Add attributes to WooCommerce product with PHP

Question

I am trying to add a new attribute with multiple values to an existing WooCommerce product.

This is the code I am using. I simplified it a bit to make it more clear.

$productId = 87356;

$attr = get_post_meta( $productId, '_product_attributes', true );

$gears = [ '3', '7' ];

$attr['pa_aantal-versnellingen'] = [
    'name' => 'pa_aantal-versnellingen',
    'value' => implode(' | ', $gears),
    'is_visible' => '1',
    'is_variation' => '1',
    'is_taxonomy' => '1'
];

update_post_meta( $productId, '_product_attributes', $attr );

foreach ( $gears as $gear ) {
    wp_set_object_terms( $productId, $gear, 'pa_aantal-versnellingen', true );
}

The attribute appears in the list of attributes on the product. However the terms are not added.

The terms also do exist in the DB:

What do I do wrong? I did a lot of research, read some other questions but they didn't help me.

Create new product attribute programmatically in Woocommerce

Answer 1

After studying the WordPress ERD I came up with a workaround.

Instead of wp_set_object_terms(); I use plain MySQL queries.

1. Get the term_taxonomy_id values from the wp_term_taxonomy table

   $placeholders = array_fill( 0, count( $gears ), '%s' );
   $format = implode( ', ', $placeholders );
   
   $sql = 
       "SELECT tt.term_taxonomy_id" .
       "FROM {$wpdb->prefix}term_taxonomy tt" .
       "JOIN {$wpdb->prefix}terms t ON tt.term_id = t.term_id" . 
       "WHERE tt.taxonomy = 'pa_aantal-versnellingen' AND t.name IN($format)"
   ;
   
   $termTaxIds = $wpdb->get_results( $wpdb->prepare( $sql, $gears ), ARRAY_N );
   

2. For each term_taxonomy_id value, insert a new entry into the wp_term_relationships table

   foreach ( $termTaxIds as $termTaxId ) {
       $insertSql = 
           "INSERT INTO {$wpdb->prefix}term_relationships" .
           "(object_id, term_taxonomy_id, term_order)" .
           "VALUES (%d, %d, 0)"
       ;
   
       $wpdb->query( $wpdb->prepare( $$insertSql, $productId, $termTaxId[0] ) );
   }