can I get some documents from firestore simultaneously using Promise.all?

Question

I want to get some documents from Firestore. in my callable cloud function, instead of waiting getting document one by one, await one by one, I use Promise.all so I can get all documents faster, like this

        const promises = []

        upcomingEventIDs.forEach( upcomingEventIDs => {

            const p = db.collection("events")
            .where("eventID","==",upcomingEventIDs)
            .where("isActive","==",true)
            .where("hasBeenApproved","==",true)
            .where("isCancelled","==",false)
            .get()

            promises.push(p)
        })

        const latestEventDataSnapshot = await Promise.all(promises)

and then I want to loop the document snapshots I just get, and here is the problem

    latestEventDataSnapshot.docs.forEach( doc => { // <-- error in this line

        

    })

I have an error

TypeError: Cannot read property 'forEach' of undefined

what is wrong in here ? what should I do to get the documents that I just get from Firestore ?

Yes, you can, but you get an array, which doesn't itself have a docs property. — jonrsharpe

Renaud Tarnec Renaud Tarnec · Accepted Answer · 2020-08-14T08:04:24

The get() method returns a Promise that resolves with a QuerySnapshot.

Since Promise.all() "returns a single Promise that resolves to an array of the results of the input promises", latestEventDataSnapshot is an Array of QuerySnapshots and you need to loop over it, for example as follows:

    const latestEventDataSnapshot = await Promise.all(promises)

    latestEventDataSnapshot.forEach(querySnapshot => {

        querySnapshot.docs.forEach(queryDocumentSnapshot => {

            console.log(queryDocumentSnapshot.data());
            //...

        })

    })

can I get some documents from firestore simultaneously using Promise.all?

1 Answers