Append element to Firebase Array

Question

How I could append an element to an array like that:

Using this code I'm overriding the old data:

let toUpdate = [book.id]
self.refUsers.child(localUser.key!).child("booksPurchased").setValue(toUpdate, withCompletionBlock: { (error, _) in

Answer 1

In this case, you will have to read the existing data, then write it back with the new value added. Arrays like this are not always the best way to store lists of data if you want to perform a lot of append operations. For that, you're better off pushing data into a location using childByAutoId.

Answer 2

You could use this method: firebase.firestore.FieldValue.arrayUnion()

Example with angularfire2:

this.afs.collection('collection').doc(id).update( {
   array: firebase.firestore.FieldValue.arrayUnion( 'newItem' )
});

For more information: https://firebase.google.com/docs/reference/js/firebase.firestore.FieldValue#arrayunion

Answer 3

You could set the values of the keys in the array to true, and then set the value directly in an update.

So if 'newId' is the new item to add, maybe something like:

const update = {
   [`/users/${localUser.key}/booksPurchased/${newId}`]: true]
}
firebase.db.ref().udpate(update);

Firebase docs example of an update: https://firebase.google.com/docs/database/web/read-and-write