Firebase Firestore: Merge a new array into an array stored in a document?

Question

here is what I am trying to do:

There is an array k, stored under 'posts' index under the below document:
```
k=['a','b',c']

firebase.firestore().collection('posts').doc(uid)
```
Merge the below array to the existing array:
```
k=['c','d']
result=['a','b','c','d','e']
```

Is there a built-in syntax to do this in Firestore? I tried arrayUnion() method, like below, but it seems that it can insert a single element, not an actual array:

   firebase.firestore().collection('posts').doc(uid).update({
        posts: firebase.firestore.FieldValue.arrayUnion(k)
   })

Any idea on how to do this? Thanks a lot in advance!

`SetOptions.merge` might help in you're case add it in the update field. — CodeRED Innovations, Jul 20 '20 at 10:49
Does this answer your question? [How to update an "array of objects" with Firestore?](https://stackoverflow.com/questions/46757614/how-to-update-an-array-of-objects-with-firestore) — Chris32, Jul 22 '20 at 13:57

score 1 · Answer 1 · 2020-07-20T11:03:53.100

1

You try some like this

firebase.firestore().collection('posts').doc(uid).set({k: this.k}, {merge: true})

set with merge: true, if document or field in document exist is updated if not is created

edited Jul 20 '20 at 11:03

answered Jul 20 '20 at 10:58

score 0 · Answer 2 · answered Sep 29 '20 at 08:52

There is a breaking change in the Firebase Firestore you have to use the new way to set the merge key. I am doing this in dart as follows you can try this way hope it will work for you

FirebaseFirestore.instance
        .collection('ABC')
        .doc({uid})
        .set(data, SetOptions(merge: true));

Firebase Firestore: Merge a new array into an array stored in a document?

2 Answers2