i have a product listing website, all products are uploaded from csv. i have a two custom field named "old_price" and "new_price".

Sometimes there is no discount (new_price) , so the field be empty. i would like to store the value of "old_price" in "new_price" , If "new_price" is empty.

its important that it get stored in database automatically, No alternate Solution please.

thanks in advance.


Assuming your products are custom posts you can do it like this:

add_action('wp_insert_post', 'do_stuff'); // when product is created
add_action('save_post', 'do_stuff' ); // on product update
   function do_stuff( $post_id ) {

       // Making sure this runs only for products
       $slug = 'product_post';
       if ( $slug != $_POST['post_type'] ) {

       if (!get_post_meta( $post_id, 'new_price', true )){
          $old_price = get_post_meta( $post_id, 'old_price', true );
          update_post_meta($post_id, 'new_price', $old_price);    


Update old products

Let's update them by 50.

// url: site.com/test-page?offset=0, change this by 50 (0,50,100,150,200,250...)

$offset = $_GET['offset']; // start with 0
$args = [
         'offset'         => $offset,
         'posts_per_page' => 50, 
         'post_type'      => 'product_post'

$the_query = new WP_Query( $args );

   foreach($the_query->posts as $product){

      if (!get_post_meta( $product->ID, 'new_price', true )){
         $old_price = get_post_meta( $product->ID, 'old_price', true );
         update_post_meta($product->ID, 'new_price', $old_price);    


   echo 'Done!';
  • will this update the old post also. – user2506619 Aug 30 '14 at 17:44
  • You mean the old_price? – Erevald Aug 30 '14 at 18:02
  • No, old post (products) which i have created before. will this function update its "new_price" too. – user2506619 Aug 30 '14 at 18:10
  • No, this runs when a product is created or updated. To change old products you can just update them with batches. I'll update my answer. – Erevald Aug 30 '14 at 19:31
  • thank you lot, its simple and does the job perfectly..thanks once again. – user2506619 Aug 30 '14 at 20:20

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