Received an exception FAILED_PRECONDITION: The query requires an index [duplicate]

Answer 1

As the exception states, you must create an index for the query you are performing.

FAILED_PRECONDITION: The query requires an index. You can create it here: {some link}

The link provided by the exception, when entered into a browser will load the Firebase Console with all the details you need to create the index needed for the query. So you just need to visit the link and follow the instructions.

Answer 2

Firebase firestore have mainly 2 types of queries

1. Simple queries
2. Compound queries

---

1. Simple queries have only where condition, so they don't need database indexes, like

FirebaseFirestore.getInstance().collection("cities")
        .whereEqualTo("capital", true)
        .get()
        .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()) {
                    for (QueryDocumentSnapshot document : task.getResult()) {
                        Log.d(TAG, document.getId() + " => " + document.getData());
                    }
                } else {
                    Log.d(TAG, "Error getting documents: ", task.getException());
                }
            }
        });

2. Your query is compound query which has multiple Where queries chained together which needs composite index, you can either create composite index in firebase console or create composite index using error message, creating index using error message is easier one, which is printed in your log message, as it handles the fields and sorting order and directly creates index for you