Promise inside forEach loop within promise, bad firebase database design?

Question

Im bulding a shopping cart with Firebase, when a user have paid a function triggers and I get all the items from the cart then I create and array of products Id's (pids) after that, I want to search the store ID of each item to notify them.

The store ID is a child in the product node. Products->{pid}->sid

This is how I do after getting the pids

.then(snap => {
        return pids.forEach( pids => {
            productIdRef = root.child(`/products/${pids}`);
             //Here I should create a promise to get the Stores Ids:
             // productIdRef.once("value")....
        });

That is nesting promises and as far as I know is not good.

So is there something I could do to avoid nesting promises or is this doomed from the beginning due to a bad Firebase database design?

Update: complete function:

    var itemsRef = NOTIFICATION_SNAPSHOT.adminRef.parent.child('items');
    var pids = [];
    return itemsRef.once('value').then(snapshot => {
        return snapshot.forEach((childSnapshot) => {
         pids.push(childSnapshot.key);
        });

    }).then(snap => {
        return pids.forEach(pids => {
            productIdRef= root.child(`/products/${pids}`).once('value');

        });

    }).catch(error => {
        // Something went wrong.
        console.error(error);
      });

Answer 1

I'm not sure what you mean by nested

Perhaps use Promise.all like below:

.then(snap => {
    return Promise.all(pids.map(pid => {
        return root.child(`/products/${pid}`);
    }));
}).then((storeIds) => {
    // result of root.child()
});