Advance Add attributes to WooCommerce product. Does not use global Attribute Taxonomy. Ensures attribute values are unique.

sample_advance_add_attributes_to_wc_product.php

/**
 * Add product attributes to Main/Parent product.
 *
 * Can add an array of attributes with an array of their respective values.
 * Will check if product attribute exist. If so, will ensure attribute values are unique.
 *
 * @param int $post_id           	Parent Product ID.
 * @param array $attr_names_values 	Array of product attributes with array of values.
 */
public function add_product_attributes( $post_id, $attr_names_values )
{
	wp_set_object_terms ($post_id, 'variable', 'product_type');

	/* Get existing _product_attributes. */
	$current_attr = get_post_meta( $post_id, '_product_attributes' );

	$attr_data = array();
	/* Loop through each attribute */
	foreach ( $attr_names_values as $attr_name => $attr_values )
	{
		/* Prepending 'pa_' to attribute key. Gonna skip the prefix for now. */
		//$attr_sanitized_name = 'pa_' . sanitize_title( $attr_name );
		$attr_sanitized_name = sanitize_title( $attr_name );

		$new_attr_values = $attr_values;
		$current_attr_values = $new_attr_values;

		if ( isset( $current_attr[0] ) )
		{
			$current_attr_values = explode( '|', $current_attr[0][ $attr_sanitized_name ]['value'] );

			/**
			 * Check is new attribute value already exist in current attribute values,
			 * if NOT exist, add in to the list.
			 * Skip if YES.
			 */
			if ( array_key_exists( $attr_sanitized_name, $current_attr[0] ) )
			{
				foreach ($new_attr_values as $new_attr_value) {
					if ( ! in_array( $new_attr_value, $current_attr_values ) )
						$current_attr_values[] = $new_attr_value;
				}
			}
		}


		/* Construct attribute data array and group them up. */
		$attr_data += array(
			$attr_sanitized_name => array(
				'name'			=> $attr_name,
				'value'			=> implode( '|', $current_attr_values ),
				'is_visible' 	=> 1,
				'is_variation' 	=> 1,
				'is_taxonomy' 	=> 0,
				'position' 		=> 0,
			)
		);
	}
	update_post_meta( $post_id, '_product_attributes', $attr_data, FALSE );
}