Work around firestore document size limit?

Question

I need to store a large number of fields, like for a star rating system, but firestore only allows 20,000 fields per document. Is there a known way around this? Right now I am going to 'shard' the fields in multiple documents, and keep the size of each document in a documentSizeTracker document that I use to determine which document to shard to (and add to the counter with a transaction). Is this the correct approach? Any problems with this?

Answer 1

Sharding certainly could work. It's hard to say without knowing exactly what kind of data you'll need from your document, and when, but that's certainly a reasonable option. You could also consider having a parent "summary" doc that contains fields you might want to search on and then split all of your data into several documents inside a subcollection of that parent.

One important nuance here: the limit isn't 20,000 fields, but 20,000 indexed fields. So if you're storing a bunch of data inside your document, but you know that you're not going to be searching on all of them, another alternative is to mark some of your fields as unindexed (which you can now do in the Firebase console in the "Exemptions" section).

If you're dealing with thousands of fields, though, you probably won't want to exempt them all one at a time, so a better alternative might be to place your data as a map inside a container field (named something like "allOfMyData"), then just mark that one field as unindexed. That will automatically remove all indexes from any fields contained inside that map.