CODEWITHSUNDEEP
androidfirebaseandroid-studiogoogle-cloud-firestoreandroid-database
Rohit Lakhotia
Rohit Lakhotia

Reputation: 81

How unique are document id of Firestore? Considering more than million document

I am trying to get the auto-generated ID from the DocumentReference Object

DocumentReference docref = db.collection("users").document(); 
String ID = check.getID();

The question is since the ID's are generated at client side there can be chances that 2 ID in firestore are similar to each other when their are more than a million document in a collection and when I use .set() the document gets updated. I have seen other answer but none solved my doubt.

Upvotes: 1

Views: 746

Answers (1)

samthecodingman
samthecodingman

Reputation: 26226

At the time of writing, a Firestore Auto ID (at least in the JavaScript SDK) is constructed from 20 random characters selected from the characters a-z, A-Z and 0-9 - so 20 characters chosen from 62 possible characters.

This means that there are 62^20 (or 7.01e35) different possible combinations.

This is very similar to the 2^120 possible combinations used in the Realtime Database (that also use the - and _ characters for 64^20 possible combinations).

The main difference between RTDB's Push IDs and Firestore's Auto IDs is that the auto ids are not encoded according to the device timestamp - all ~120 bits are random.

So, statistically it is very unlikely that you will encounter a collision. But you can always use your own system to generate your own IDs or use some drop in uuid package to generate a 128-bit or greater ID.

Upvotes: 4

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