Creating WooCommerce product variation adds an empty attribute value

When adding variations to a WooCommerce product it is adding in a blank attribute. Meaning that when I try to add in my own attribute it gets appended to an existing array.

Example code I am running:

$product_variation = wc_get_product( $variation_id );
$product_variation->set_attributes(array('attribute_pa_varinfo' => 'blue'));
$product_variation->save();

Then when I var_dump($product_variation); I get the following:

["attributes"]=>
array(2) {
  [0]=>
  string(0) ""
  ["pa_varinfo"]=>
  string(4) "5034"
}

So when I view the product in WooCommerce admin all my variations are there but the attribute is stuck at “any option” for all of them.

The weird thing is when I then “update” the product from wp-admin all of the variations then get the correct attribute selected.

Has anyone encountered this before or got any ideas of what I can do?

As another example if I run the following:

$product_variation = wc_get_product( $variation_id );
$product_variation->set_attributes( array ( 'simon' => 'confused' ) );
$product_variation->save();
var_dump($product_variation->get_attributes());

This returns:

array(2) {
 [0]=> string(0) ""
 ["simon"]=> string(8) "confused"
}

Where does the first item come from? I can’t seem to clear it.

Answer

So it turns out the problem was with the actual setting up of the attribute against the main parent product, I was passing through an unnamed array, by adding wc_attribute_taxonomy_name('varinfo') => (line 2 below) this correctly saves the data and removes the blank array I had.

      $product_attributes = array(
      wc_attribute_taxonomy_name('varinfo') => 
      array (
        'name'         => wc_attribute_taxonomy_name( 'varinfo' ), // set attribute name
        'value'        => '', // set attribute values
        'position'     => 1,
        'is_visible'   => 1,
        'is_variation' => 1,
        'is_taxonomy'  => 1
      )
    );

    update_post_meta($post_id, '_product_attributes', $product_attributes);