Set max quantity based on a custom field in a Product Variation

Question

I am trying to set a variation's maximum quantity allowance based on the value of a one of its custom fields.

Everything is good - the code is working below, however rather than $quantity = round(9/3); I want the value to be $quantity = round($quantity/$weight);

The issue I am having (and have had numerous times in the past with other functions) is that I can't for the life of me seem to pull the correct 'Custom_Field' data. Everything I try returns either boolean false or string Length(0). When I do a var_dump($variation_ID) I get a ton of data, but my custom field is not there.

This is strange, because the data is pulled in other functions I have - but not in this situation and I can't figure out why.

// On single product pages
    add_filter( 'woocommerce_available_variation', 'customizing_available_variation', 10, 3  );
    function customizing_available_variation( $args, $product_id, $variation_id ) {


    $product = wc_get_product ( $product_id );
    $weight = get_post_meta( $variation_ID, 'custom_field', true );

    $product_stock = $product_id->get_stock_quantity();
    var_dump($variation_id);

    $quantity = round(9/3);

    if( is_woocommerce() ){
        $args['max_qty'] = $quantity;
    }

    return $args;
}

Answer 1

woocommerce_available_variation passes three arguments, the third one being a WC_Product_Variation (that's why you're getting a ton of data when var_dump-ing it).

You've named your third argument $variation_id, which probably led you to treating it as a post/product id.

Meaning, you're trying to pass a WC_Product_Variation as an id to get_post_meta():

$weight = get_post_meta( $variation_ID, 'custom_field', true );

You're also doing the same thing for the second argument (which is the product, not the product id).

You just have to get the variation id and pass that instead:

/**
 * Customize available variation
 *
 * @param array $args
 * @param WC_Product_Variable $product
 * @param WC_Product_Variation $variation
 */
function customizing_available_variation( $args, $product, $variation ) {
    $weight = get_post_meta( $variation->get_id(), 'custom_field', true );
    // …
}