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This is a very basic question but I'm not sure if I understand this correctly, and I didn't find sources that completely clarified it for me.

Firestore documents are always saved in collections. And a collection can have as many documents as you want, but every document has a max size of 1MB.

I've seen that subcollections must be created this way:

DocumentReference messageRef = db
    .collection("rooms").document("roomA")
    .collection("messages").document("message1");

So we have a collections messages UNDER a document roomA. So therefore the max size for the whole (sub) collection messages should also be 1 MB since it is a child from a document, so everything stored in messages is also stored in roomA.

Therefore you couldn't save that many douments in messages.

Or do I understand this wrong?

I've also read that Firestore is shallow. Would this mean in this case, that a document stored in messages is NOT also stored in the parent document roomA?

In that case you could have as many sub-collections of roomA as you want, as long as their names added up are less than 1 MB in total?

And each of these sub-collections itself can have as many documents as you want.

Which is right?

mathematics-and-caffeine
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1 Answers1

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I think this question is answered here: https://stackoverflow.com/a/48337444/7545496

In short: a subcollection has no effect on the containing document's size and can have an arbitrary number of elements (each of which has a size limit of 1MB)

Steffen Frank
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