Current Orders Cache Query implementation results in more queries than when disabled.

[prettyboymp]

Prerequisites

• I have carried out troubleshooting steps and I believe I have found a bug.
• I have searched for similar bugs in both open and closed issues and cannot find a duplicate.

Describe the bug

Querying a set of orders with orders_cache_usage_is_enabled() === true results in more queries than when it is disabled when querying a set of orders by ID.

Because the WC_Data::__sleep() method only stores the ID, the WC_Data::__wakeup() method is set to run the initial object constructor again. For orders, this results in two queries being run for each order requested - one for the order data and one for meta.

When caching is disabled, the data for the set of orders and meta can be retrieved for all orders in two queries.

Expected behavior

The expectation behind cached orders is that a successful cache hit of an order would not result in a DB read being made.

Actual behavior

A successful cache hit for an order requires two DB reads because only the ID is stored in cache.

Steps to reproduce

1, Setup an environment with multiple orders and note the IDs.
2. Disabled the orders_cache_usage_is_enabled feature flag.
3. Setup a script to test the number of queries run, e.g.:

$order_ids = [ 1, 2, 3, 4 ];
WC_Order_Factory::get_orders( $order_ids );
$final_query_count = count( $wpdb->queries );
WP_CLI::success( 'Queries run: ' . ( $final_query_count - $initial_query_count ) );

4. Enable the orders_cache_usage_is_enabled feature flag.
5. Visit the orders listing admin page to prime cache.
6. Run the previous script again.

WordPress Environment

WPCOM

Isolating the problem

• I have deactivated other plugins and confirmed this bug occurs when only WooCommerce plugin is active.
• This bug happens with a default WordPress theme active, or Storefront.
• I can reproduce this bug consistently using the steps above.

[prettyboymp]

This will likely require reworking the __sleep() / __wakeup() handling within WC_Data. They were originally added because the data objects stored references to more than just raw data, e.g. the datastores which shouldn't be cached.