Cloud Firestore collection count

Question

Is it possible to count how many items a collection has using the new Firebase database, Cloud Firestore?

If so, how do I do that?

Answer 1

This uses counting to create numeric unique ID. In my use, I will not be decrementing ever, even when the document that the ID is needed for is deleted.

Upon a collection creation that needs unique numeric value

1. Designate a collection appData with one document, set with .doc id only
2. Set uniqueNumericIDAmount to 0 in the firebase firestore console
3. Use doc.data().uniqueNumericIDAmount + 1 as the unique numeric id
4. Update appData collection uniqueNumericIDAmount with firebase.firestore.FieldValue.increment(1)

firebase
    .firestore()
    .collection("appData")
    .doc("only")
    .get()
    .then(doc => {
        var foo = doc.data();
        foo.id = doc.id;

        // your collection that needs a unique ID
        firebase
            .firestore()
            .collection("uniqueNumericIDs")
            .doc(user.uid)// user id in my case
            .set({// I use this in login, so this document doesn't
                  // exist yet, otherwise use update instead of set
                phone: this.state.phone,// whatever else you need
                uniqueNumericID: foo.uniqueNumericIDAmount + 1
            })
            .then(() => {

                // upon success of new ID, increment uniqueNumericIDAmount
                firebase
                    .firestore()
                    .collection("appData")
                    .doc("only")
                    .update({
                        uniqueNumericIDAmount: firebase.firestore.FieldValue.increment(
                            1
                        )
                    })
                    .catch(err => {
                        console.log(err);
                    });
            })
            .catch(err => {
                console.log(err);
            });
    });