How can I CORRECTLY append map array to firestore?

Question

I want to add Map<> data to my firestore database with code :

Map<String, Object> prop = {
  'read' : true,
  'vote_left' : false,
  'vote_right' : false,
};
Map<String, Object> attended_topic =
{
  received_id:prop
};

FirebaseFirestore.instance.collection('userinfo').doc(user_now!.uid)
    .update({"attended_topic": FieldValue.arrayUnion([attended_topic])});

What I expected is this.

attended_topic
  topicId_0
    read : true 
    vote_left : false
    vote_right : false

But I got something unexpected.

attended_topic
  0
    topicId_0
      read : true 
      vote_left : false
      vote_right : false

I never expected that new category '0' appearing and donot know why. Since the atabase has other properties so I thought using update() rather than set() is adequate. Please somebody tell my why this happens.

Peter Obiechina · Accepted Answer · 2022-08-28 11:10:07Z

2

From the docs FieldValue.arrayUnion adds elements to an array but only elements not already present.

So {"a": FieldValue.arrayUnion([b])} adds b variable to the Array a.

To solve your problem, just remove FieldValue as shown below.

FirebaseFirestore.instance
    .collection('userinfo')
    .doc(user_now!.uid)
    .set({"attended_topic": attended_topic}, SetOptions(merge: true));
// use set method to add new data (not update)
// or

FirebaseFirestore.instance.collection('userinfo').doc(user_now!.uid).set(
  {
    'attended_topic': {
      received_id: {
        'read': true,
        'vote_left': false,
        'vote_right': false,
      }
    }
  },
  SetOptions(merge: true),
);

edited Aug 28, 2022 at 11:10

answered Aug 28, 2022 at 10:19

Peter Obiechina

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2 Comments

MooNChilD Song Over a year ago

It seems that set() removes all other data in the target doc. Can you please suggest me some supplementary ?

Peter Obiechina Over a year ago

Simply use SetOptions(merge: true). I will update my answer to show this.

MooNChilD Song · Accepted Answer · 2022-08-28 11:08:20Z

1

I solved this problem referring Peter's solution and changing it slightly.

FirebaseFirestore.instance.collection('userinfo').doc(user_now!.uid)
    .set({"attended_topic": attended_topic}, SetOptions(merge: true));

answered Aug 28, 2022 at 11:08

MooNChilD Song

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