How to efficiently add items to collection with firebase firestore

Question

I have an array of tags that I would like to add to a firestore collection.

If I'm not misunderstanding the approach I have here, I think I'm making individual adds to the collection when I think it would be more efficient to 'group' them and set them all at once. Is something like this possible? Also would it be possible to add the document to the workouts collection at the same time?

Right now I'm looking at tags.length + 1 writes to firebase for every call to this function. I'd like to reduce that as much as possible.

logWorkoutAsync({ userId, timeStamp, tags }){
    var db = this.firebase.firestore();

    return db.collection('users').doc(userId).collection('workouts').add({
        timeStamp,
        'class': false
    }).then(doc => {

        var tagsCollection = doc.collection('tags')

        var promises = []

        tags.forEach(t => {
            promises.push(tagsCollection.doc(t.id.toString()).set(t))
        })

        return Promise.all(promises)
    })
}

Answer 1

Cloud Firestore has support for batched writes, see the docs here: https://firebase.google.com/docs/firestore/manage-data/transactions

So you could do something like this:

logWorkoutAsync({ userId, timeStamp, tags }){
    var db = this.firebase.firestore();

    return db.collection('users').doc(userId).collection('workouts').add({
        timeStamp,
        'class': false
    }).then(doc => {

        var tagsCollection = doc.collection('tags');

        // Begin a new batch
        var batch = db.batch();

        // Set each document, as part of the batch
        tags.forEach(t => {
            var ref = tagsCollection.doc(t.id.toString());
            batch.set(ref, t);
        })

        // Commit the entire batch
        return batch.commit();
    })
}

Answer 2

IF you want to add multiple documents to collection you could do something like this which worked fine for me since I was stuck in a similar case.

let colRef = db.collection('cars')

/// Batch Thing //
var batch = db.batch();

let cars = [{name: 'Audi', model: 'A8'}, {name: 'BMW', model: '730'}]
cars.forEach(c => {
  let ref = colRef.doc(`${c.name}`)
  batch.set(ref, {
    name: `${c.name}`,
    model: `${c.model}`
  })
})

return batch.commit()
  .then(data => {
    console.log('good')
  })
  .catch(error => {
    console.log('there is an error')
  })