Firebase Swift - How to create a child and add its id to another ref property?

Question

As described here, I'd like to store Book objects in a separate ref and store its id value inside books property of User

Users:
user_id:121jhg12h12
  email: "[email protected]"
  name: "John Doe"
  profile_pic_path: "https://...".
  language: "en"
  exp_points: 1284
  friends: [user_id]
  books: [[book_id, status, current_page, start_date, finish_date]]
  badges: [[badge_id, get_date]]

Books:
book_id: 3213jhg21
  title: "For whom the bell tolls"
  author: "Ernest Hemingway"
  language: "en"
  pages_count: 690
  ISBN: "21hjg1"
  year: 2007

Whenever I add a book inside the app

self.ref!.child("Books").childByAutoId().setValue(["title": arrayOfNames[0] as! NSString, "author": arrayOfNames[1] as! NSString , "pages_count":arrayOfNames[2] as! NSString])

The book object is created in Books ref, but I'd like to add its id to the User's books array of user right away.

Can it be done in some nifty way, instead of querying the book, retrieve its ID and add it to the array?

If no, what's the proper way o querying the object id that has been just created?

Maybe I should not use AutoId mode and create unique Id for each object by myself in app?

Answer 1

You can get the key created by childByAutoId in this way:

let newBookRef = self.ref!
                      .child("Books")
                      .childByAutoId()

let newBookId = newBookRef.key

---

let newBookData = [
  "book_id": newBookId,
  "title": arrayOfNames[0] as! NSString,
  "author": arrayOfNames[1] as! NSString,
  "pages_count":arrayOfNames[2] as! NSString
]

newBookRef.setValue(newBookData)