Firebase Firestore how to add subcollection

Question

Hi I'm new to programming and have been working on a website using Firebase Firestore as my database.

I wanted to create a subcollection in my already existing collection ('Einkaufsliste') by using the document ID. But instead it creats a new document with a different document ID and a subcollection. Using a onClick methode to create the cart. The counter is for checking if the current user ID already exists

Hier ist my JavaScript code

function clickCart() {
var docID = '';
var user = firebase.auth().currentUser;
console.log(counter)
if(counter < 1) {
    console.log('DocID: ' + docID);
    firebaseDatabase.collection('Einkaufsliste').doc().set({
        UserID: user.uid,
        UserName: user.displayName
    })
    .then(() => {
        console.log("%c Document successfully written!", 'color: green' );
        counter = counter + 1
    })
    firebaseDatabase.collection('Einkaufsliste').where('UserID', '==', user.uid).get()
    .then((snapshot) => {
        snapshot.docs.forEach(documentUserUi => {
            console.log('Function works!')
            console.log(documentUserUi.id);
            docID = documentUserUi.id;
            console.log('DocID: ' + docID);

        })
    })
    console.log("hier!")
    console.log('DocID: ' + docID);
    firebaseDatabase.collection('Einkaufsliste').doc(docID).collection('Warenkorb').doc().set({
        WarenkorbName: 'test'
    })

} else {
    console.log("%c User already exists and can't be added", "color: yellow")
    console.log(counter)

}

}

Edit I think that I found the problem docID seems to be empty, but still need to test. Also for some reason console.log('hier') output is earlier than the console.log('Funktion works!')

Answer 1

The .set() accept an object as parameter and cannot be null. You would have provide a document ID as shown below:

firebaseDatabase.collection('Einkaufsliste').doc(docID).collection('Warenkorb').doc("someDocumentId").set({
        WarenkorbName: 'test'
    })

But if you are not concerned about document ID then you can use a random ID that firestore generates by using the .add() method:

firebaseDatabase.collection('Einkaufsliste').doc(docID).collection('Warenkorb').add({
        WarenkorbName: 'test'
    })

Answer 2

For Firebase 9 here is an example that works:

import { db } from "../firebase"; // your local firebase.js
import { addDoc collection } from "firebase/firestore";

const docRef = await addDoc(
      collection(db, "users", "sadasdsdasas", "posts"),
      {
        description: "test Description",
        title: "Test",
      }
    );


console.log("Document written with ID: ", docRef.id);

details:
"users" => parentCollection
"sadasdsdasas" => parent collection id
"posts" => subCollection to into the user with the id "sadasdsdasas"

doc: https://firebase.google.com/docs/firestore/data-model