如何在 Firebase / Firestore 中创建用户时创建嵌套集合，用户可以在其中保存已添加书签的项目

Question

I want to be able to have a nested collection in firebase/firestore where I can save an authenticated users favorites. I was trying to create the collection when the user is created so I can just read/write to it later but I can't figure out how to create the collection. I have something like this:

//This function creates a new user. If the user already exists, no new document will be created
export const createUserDocumentFromAuth = async (
  userAuth,
  additionalInfo = {}
) => {
  if (!userAuth) return;

  const userDocRef = doc(db, 'users', userAuth.uid); //database instance, collection, identifier
  const bookmarkRef = doc(db, 'users', userAuth.id, 'bookmarks'); //This triggers error
  const userSnapshot = await getDoc(userDocRef);
  if (!userSnapshot.exists()) {
    //If user snapshot doesn't exist - create userDocRef
    const { displayName, email } = userAuth;
    const createdAt = new Date();

    try {
      await setDoc(userDocRef, {
        displayName,
        email,
        createdAt,
        ...additionalInfo,
      });
      setDoc(bookmarkRef, { //Try to create a bookmarks collection here
        favorites: []
      })
    } catch (error) {
      console.log('Error creating user', error.message);
    }
  }
  //if user data exists
  return userDocRef;
};

I can create the user just fine but not another collection at the same time. I also tried just creating the collection when a signed-in user clicks on the bookmark button like this but I get a type error in both cases Uncaught (in promise) TypeError: n is undefined every time.

export const addBookmarkForUser = async (userAuth, showId) => {
  const bookmarkRef = doc(db, 'users', userAuth.id, 'bookmarks');
  try {
    await setDoc(bookmarkRef, {
      favorites: showId
    });
  }catch(error){
    console.log('error creating bookmark', error.message)
  } 
};

I'm pretty new to Firebase / Firestore and all I want is to be able to save an item id in an array for an individual user when they click a button. If saving in an array is not ideal or there is any better way to do this, I am open to any suggestions at this point.

Answer 1

I was trying to create the collection when the user is created so I can just read/write to it later but I can't figure out how to create the collection.

A (sub)collection is only created when you create the first document in it . There is no way to materialize an empty collection without a document.

And it is normal that you get an error when using the doc() method as follows

const bookmarkRef = doc(db, 'users', userAuth.id, 'bookmarks');

because this method is used to create a DocumentReference and therefore you need to pass a path with an even number of path segments. In you case you pass 3 segments.

You could very well define the CollectionReference for the bookmarks subcollection as follows, using the collection() method and passing the 3 segments

const bookmarkRef = collection(db, 'users', userAuth.id, 'bookmarks');

but, until you add a document in it, it will not exist in the database.

---

Conclusion: You will automatically create the user's bookmarks subcollection the first time you create a bookmark for the user.

For example:

const bookmarksCollectionRef = collection(db, 'users', userAuth.id, 'bookmarks');
await bookmarksCollectionRef.add({ ... })