Is there a way to add a .then promise to a for Loop?

May 11, 2023

I am working on a Firebase cloud function to update a field value for every element of the array I provide.

Below is my loop.

I would like for it to add a document to another collection as soon as this loop has been completed.

// FOR EACH ITEM
sortedArray.forEach(([key, val]) => {
    walletRef.doc('j10wmCUhUWPxYJpIElBxmFAEI6l1').update({
        [val.product]: admin.firestore.FieldValue.increment(val.quantity),
    })
})

When I try to add a .then like below, it fails

// FOR EACH ITEM
sortedArray.forEach(([key, val]) => {
    walletRef.doc('document_id_here').update({
        [val.product]: admin.firestore.FieldValue.increment(val.quantity),
    })
}).then((doc) => {
    logsRef.add({
        user_id: "document_id_here",
        product: items,
        transactionType: "purchase",
        date: new Date(),
    })
});

Logged error:

textPayload: "Function execution took 2594 ms, finished with status: 'crash'"

The field values are updated but the new document is not created.
Please help.
Thanks.

>Solution :

Your update loop seems unnecessary since you’re performing the operations on the same document.

Try something like this instead, setting multiple properties at once

walletRef
  .doc("document_id_here")
  .update(
    Object.fromEntries(
      sortedArray.map(({ product, quantity }) => [
        product,
        admin.firestore.FieldValue.increment(quantity),
      ])
    )
  )
  .then((writeResult) => {
    // ...
  });

From the docs for Increment a numeric value…