firebase firestore addding new document inside a transaction - transaction.add is not a function

Question

I was assuming that it was possible to do something like:

transaction.add(collectionRef,{
  uid: userId,
  name: name,
  fsTimestamp: firebase.firestore.Timestamp.now(),
});

But apparently it is not:

transaction.add is not a function

The above message is displayed inside the chrome console.

I see that we can use the set method of the transaction to add a new document transactionally. see: https://firebase.google.com/docs/firestore/manage-data/transactions

The thing is if I use set instead of add(which is not supported anyways), the id of the document should be created by me manually, firestore won't create it. see: https://firebase.google.com/docs/firestore/manage-data/add-data

Do you see any downside of this not having an add method that generates the id for you automatically?

For example, is it possible that the id generated by the firestore itself is somehow optimized considering various concerns including performance?

Which library/method do you use to create your document IDs in react-native while using transaction.set?

Thanks

Answer 1

If you want to generate a unique ID for later use in creating a document in a transaction, all you have to do is use CollectionReference.doc() with no parameters to generate a DocumentReference which you can set() later in a transaction.

(What you're proposing in your answer is way more work for the same effect.)

// Create a reference to a document that doesn't exist yet, it has a random id
const newDocRef = db.collection('coll').doc();

// Then, later in a transaction:
transaction.set(newDocRef, { ... });

Answer 2

after some more digging I found in the source code of the firestore itself the below class/method for id generation:

export class AutoId {
  static newId(): string {
    // Alphanumeric characters
    const chars =
      'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    let autoId = '';
    for (let i = 0; i < 20; i++) {
      autoId += chars.charAt(Math.floor(Math.random() * chars.length));
    }
    assert(autoId.length === 20, 'Invalid auto ID: ' + autoId);
    return autoId;
  }
}

see: https://github.com/firebase/firebase-js-sdk/blob/73a586c92afe3f39a844b2be86086fddb6877bb7/packages/firestore/src/util/misc.ts#L36

I extracted the method (except the assert statement) and put it inside a method in my code. Then I used the set method of the transaction as below:

generateFirestoreId(){
        const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
        let autoId = '';
        for (let i = 0; i < 20; i++) {
            autoId += chars.charAt(Math.floor(Math.random() * chars.length));
        }
        //assert(autoId.length === 20, 'Invalid auto ID: ' + autoId);
        return autoId;
    }

then,

newDocRef = db.collection("PARENTCOLL").doc(PARENTDOCID).collection('SUBCOLL').doc(this.generateFirestoreId());
                        transaction.set(newDocRef,{
                            uid: userId,
                            name: name,
                            fsTimestamp: firebase.firestore.Timestamp.now(),
                        });

Since I am using the same algo for the id generation as the firestore itself I feel better.

Hope this helps/guides someone.

Cheers.

Answer 3

Based on the answer from Doug Stevenson, this is how I got it worked with @angular/fire:

// Create a reference to a document and provide it a random id, e.g. by using uuidv4
const newDocRef = this.db.collection('coll').doc(uuidv4()).ref;

// In the transaction:
transaction.set(newDocRef, { ... });