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For the structure of my database I need to know if the automatically generated identifiers in Firebase Cloud Firestore are unique in the collection or in the whole database.
How to do that?
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New document with same ID should not be allowed in the same collection. It should be possible to fetch an already existing document from a previous import.
There is no specific API to retrieve unique values from Cloud Firestore. You will have to retrieve all relevant documents and determine the unique names in your own code. Alternatively, consider adding a document with unique names and update that with every write.
The best way to prevent duplicate nodes in firebase realtime database or duplicate documents in firebase firestore database is to keep a check in the app itself to verify that the record to be inserted doesn't already exist in the database by querying for data using key field in where clause.
The keys generated by calling add() in Firestore are not tied to the collection on which you call add(). Instead they are random identifiers that are statistically guaranteed to be unique. In the case of Firestore (and Firebase Realtime Database) these keys are generated client-side.
If you're interested, have a look at how the Firestore JavaScript SDK implements the logic:
add calls doc()
doc calls AutoId.newId()
AutoId.newId() generates a client-side ID
In itself the logic is similar to how the Firebase Realtime Database generates its push IDs. The main difference seems to be that Firestore's auto-generated keys are not based on the local timestamp, so they cannot be meaningfully used to order the documents in the collection.
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