Attach more data from firebase firestore to index object in algolia

I’m using Firebase Firestore and Algolia on a RN App. But I’m encountered with a problem. I have to build a search UI where I can show all data about the post AND some data of the user that created the post. The problem is, in firestore, posts and users are in two different collections. Tho, I have a uid field in each post doc, which is equal to a firestore doc id in users collection for other matters in the app(attaching user to post), I don’t know how to do it in Algolia. For example, I would need each index in Algolia to perform another query on firestore, on another collection, and get the objectID === uid in the index, and add it as an object inside that query.