I run a mass discount plugin, lets just say for a -50% price which works in the frontend normally. Also I tested the following scenario in Wordpress 5.5.3, woocommerce both 3.7 and 4.8 and no other plugins.

I have a function to create an xml. In that function I check and get the product parent ids and then the products as objects.

When I try to get the sale price with either $product->get_sale_price() or print the whole object print_r($product) the [sale_price] is empty, the [regular_price] is empty and the [price] returns the original price

Obviously, what I want is to run a mass discount and return the sale price of the products in my custom function.

I tried the 2 mass discount plugins 'WooCommerce Dynamic Pricing & Discounts' and 'Finale Lite'. Then tried with the official themes 2020 and 2021 and with my normal 'Elessi' theme. No results with any plugin/theme/version combination.

I also tried $product->get_variation_sale_price( 'min', true ); which returns the original price.

I guess this is because sale price is product specific. However, why this happens and how could overcome this and show the sale price if a discount is running?

$args = array(
  'post_type'             => 'product',
  'post_status'           => 'publish',
  'ignore_sticky_posts'   => 1,
  'posts_per_page'        => '1000',
  'tax_query'             => array(
    array(
      'taxonomy'      => 'product_cat',
      'field' => 'term_id',
      'terms'         => 123,
      'operator'      => 'IN'
    ),
    array(
      'taxonomy'      => 'product_visibility',
      'field'         => 'slug',
      'terms'         => 'exclude-from-catalog',
      'operator'      => 'NOT IN'
    )
  )
);
$query = new WP_Query( $args );

if ( $query->have_posts() ) {
  while ( $query->have_posts() ) : $query->the_post();
    $product = wc_get_product( $query->post->ID );

    $product_id = $product->is_type( 'variation' ) ? ( method_exists($product, 'get_parent_id') ? $product->get_parent_id() : $product->get_parent() ) : $product->get_id();

    $product_id = $product->is_type( 'variation' ) ? $product->get_parent_id() : $product->get_id();

    $product = wc_get_product( $product_id );

    $product_price= $product->get_sale_price() ? $product->get_sale_price() : $product->get_price();
    print_r($product);

  endwhile;
}