Get Random Documents from Firestore

yuyu — Mon, 03 Jun 2024 15:22:05 +0000

When working with Firestore, retrieving random elements poses a challenge because Firestore does not natively support queries for fetching documents randomly.

In addition, Firestore does not support offset queries, so it is not possible to generate a random number on the client side and then fetch documents randomly by specifying an index.

Basic Solution

Fetch all documents in the collection, shuffle the array, and then select elements either from the beginning or at random indexes.

This method is quite simple. However, if there are a large number of documents, it can be quite costly and the processing speed may become slow.

Another Approach: Changing the Way to Manage Data

This is a solution that only loads the necessary records.

Configure a property within each document that has a number assigned randomly.
When fetching documents, use an orderBy query targeting this random number property. By combining this with a limit query, it is possible to fetch a specified number of documents or even the entire collection.
After fetching the documents, assign a new random number to the random number property of each document. This step ensures that the collection remains shuffled reproducibly.

Bottleneck

This method requires a significant number of write operations. Since Firestore incurs higher costs for write operations compared to read or delete operations, frequent fetching can become costly.

Finally

I was pleasantly surprised when I first discovered this method. Despite Firestore not supplying direct queries for fetching random documents, this creative solution offers an excellent workaround.

DEV Community: yuyu

Get Random Documents from Firestore