Hey @felipeelia , from WC team here. I would love to help you with HPOS compatibility for ElasticPress. It looks like currently you hook into posts_pre_query to hijack WP query and populate results from elasticsearch, would be happy to add similar filter for HPOS as well. It seems we won't need to create new index for HPOS orders, since there is already a allowlist for what data can be synced, and we can add HPOS orders in the same index (note that we always insert a shop_order_placehold post and use the same ID in order tables, so a ID conflict won't happen).

Let us know if there is anything else you would need besides an equivalent posts_pre_query filter.

@vedanshujain you got it right. It is worth saying though that an equivalent filter for posts_pre_query would be a good start, but we will probably need some further changes, especially given the number of times the code seems to be touching the database directly.

Cool cool, we will get a PR started for posts_pre_query. Please let us know what you discover during development, we would be happy to add more action/filters where they makes sense, and especially if a similar filter already exists with the posts.

@felipeelia , I can try and give it a shot for a draft PR, if this is still on the roadmap?

To have this one done, in general steps, we need to:

1. Create a new file called OrdersHPOS.php in includes/classes/Feature/WooCommerce/
2. Conditionally call it from includes/classes/Feature/WooCommerce/Orders.php
3. Make Orders be indexed in ElasticPress posts' index
4. Use the woocommerce_hpos_pre_query filter to prevent any SQL query from being fired and use ElasticPress instead.