Creating WooCommerce product variation adds an empty attribute value

Question

When adding variations to a WooCommerce product it is adding in a blank attribute. Meaning that when I try to add 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 1

Update (related to your update and comments)

To resume (our comments): The product attribute exist. Also all terms for this attribute are defined and set in the parent variable product (in the "Attribute" settings tab)

I have made some tests:

1. I have create a new 'Varinfo" attribute (pa_varinfo) with 4 values (term names):
   104 mm, 110 mm, 130 mm and 140 mm (so term slugs are like 104-mm…).
2. I have created a new variable product with one empty variation (nothing defined for this variation) and alter saving the select field shows:
   

When using this code (similar to yours):

$parent_product = wc_get_product( 738 ); // Get the variable product
$variation_ids = $parent_product->get_children(); // Get all children variations (Here only one)

// Iterating through each variation
foreach( $variation_ids as $variation_id ){
    $variation = wc_get_product($variation_id);
    $variation->set_attributes(array('pa_varinfo' => '104-mm'));
    $variation->save();
}

it's just working for me and I get the selected value in backend for this variation:

Note that I am using the taxonomy name for the attribute and the term SLUG in the array…

So I don't know where you are doing something wrong…

---

This happens when you set an attribute term that doesn't exist and/or is not registered as a post term of the parent variable product. You can try this:

// Get an instance of the WC_Product_Variation object
$variation = wc_get_product( $variation_id );

// Initialising variables
$taxonomy = 'pa_varinfo'; // The taxonomy
$term_name = 'Blue'; // The term "NAME"

// Check if the term exist and if not we create it.
if( ! term_exists( $term_name, $taxonomy ) )
    wp_insert_term( $term_name, $taxonomy );
    
// Get an instance of the WP_Term object
$term = get_term_by( 'name', $term_name, $taxonomy );

// Get the post terms names from the parent variable product.
$post_term_names =  wp_get_post_terms( $variation->get_parent_id(), $taxonomy, array('fields' => 'names') );

// Check if the post term exist and if not we set it in the parent variable product.
if( ! in_array( $term_name, $post_term_names ) )
    wp_set_post_terms( $variation->get_parent_id(), $term_name, $taxonomy, true );

// Now you can set the term for the attribute in your variation
$variation->set_attributes( array( $taxonomy => $term->slug ) );
$variation->save(); // Registering the data

// Get an instance of the parent WC_Product_Variable object
$parent_product = wc_get_product( $variation->get_parent_id() );

// Sync the data of the variation in the parent variable product
$parent_product->sync( $variation_id );

This is tested and works

Assuming that you have already created the appended attribute in WooCommerce…, you will get:

Answer 2

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);

Answer 3

Since WC 3.0 in order to get the variation selected you should use set_default_attributes.

Instead of

$variation->set_attributes(array('varinfo' => '104-mm'));

Use

$variation->set_default_attributes(array('varinfo' => '104-mm'));