Add a product specific custom attribute. These are not attributes that will be filterable via the WooCommerce Layered Nav. These attributes are stored specifically for a product. [datafeedr]

add-custom-attribute-for-product.php

<?php

/**
 * Add the custom attribute label "Special Promotion" to a product.
 *
 * @param array $attributes An array attributes.
 * @param array $post An array of post data including ID, post_title, post_status, etc...
 * @param array $product An array of product data returned from the Datafeedr API.
 * @param array $set A post array for this Product Set with an array key of postmeta containing all post meta data.
 * @param string $action The action the Product Set is performing. Value are either "insert" or "update".
 *
 * @return array Updated $attributes array.
 */
add_filter( 'dfrpswc_product_attributes', 'mycode_set_promo_attribute_label', 20, 5 );
function mycode_set_promo_attribute_label( $attributes, $post, $product, $set, $action ) {

	// The label for the product field.
	$label = 'Special Promotion';

	// The product field to import.
	$field = 'promo';

	$sanitized_label = sanitize_title( $label );

	if ( ! isset( $product[ $field ] ) ) {
		return $attributes;
	}

	if ( isset( $attributes[ $sanitized_label ] ) ) {
		return $attributes;
	}

	if ( ! is_array( $attributes ) && empty( $attributes ) ) {
		$attributes = [];
	}

	$attributes[ $sanitized_label ]['name'] = $label;

	return $attributes;
}

/**
 * Set value for "Special Promotion" attribute.
 *
 * @param array|string $value The current value of the $attribute for this $post.
 * @param string $attribute The slug of the attribute. Examples: pa_color or pa_shoe-size
 * @param array $post An array of post data including ID, post_title, post_status, etc...
 * @param array $product An array of product data returned from the Datafeedr API.
 * @param array $set A post array for this Product Set with an array key of postmeta containing all post meta data.
 * @param string $action The action the Product Set is performing. Value are either "insert" or "update".
 *
 * @return array|string The updated attribute's value.
 */
add_filter( 'dfrpswc_filter_attribute_value', 'mycode_set_promo_attribute_value', 30, 6 );
function mycode_set_promo_attribute_value( $value, $attribute, $post, $product, $set, $action ) {

	// The label for the product field.
	$label = 'Special Promotion';

	// The product field to import.
	$field = 'promo';

	if ( ! isset( $product[ $field ] ) ) {
		return $value;
	}

	if ( $attribute == $label ) {
		return $product[ $field ];
	}

	return $value;
}