How to create and read an array of key value pairs (map) in Flutter for storing data in Firestore

Question

I have question collection and some 'X' number of fields in that, but now I want to set an array of key value pairs in existing document of my firestore collection question for storing the data in my firestore the desired structure is shown below in image, I am not able to get how to create structure like this I want to fetch them and create data in firestore using flutter and dart,

so far I am able to set string fields like this but not array of them,

 Future<void> setAnswer() async {
      String ans = ans_Controller.text;
      FirebaseFirestore db = FirebaseFirestore.instance;

      await db.runTransaction((transaction) async {
        DocumentReference qRef =
            db.collection('question').doc(widget.question.id);
        await transaction.set(
            qRef,
            {
              'content': ans,
              'timestamp': DateTime.now().toString(),
              'username': _currentUser.displayName,
            },
            SetOptions(merge: true));
      });
    }

and also every array element must have same key but different values, like a hashmap

any help is appreciated,

thank you

there's no problem in that code but that's not giving me the desired result as its for the single string and not for array of maps which I want please check the screenshot I have attached I want to do something like that how its possible to do so, I just want to append all the three fields in single array and not in one separate string fields as I have done in the given code above — Mithson
– Mithson, Commented Oct 4, 2021 at 22:57

Frank van Puffelen · Accepted Answer · 2021-10-04 23:51:43Z

1

I think you're looking for the array-union operation. To add an element to the answer array if it doesn't exist in there yet, do:

documentRef.updateData({'answer': FieldValue.arrayUnion([{
  'content': ans,
  'timestamp': DateTime.now().toString(),
  'username': _currentUser.displayName,
}])});

answered Oct 4, 2021 at 23:51

Frank van Puffelen

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7 Comments

Mithson Over a year ago

and how can I read all of the three in separate widget once I have updated them?

Mithson Over a year ago

okay I gotcha how to create one array-union but how to read it, would be very helpful if you you can show how can we read all those three fieldvalues and show them in text widget

Frank van Puffelen Over a year ago

That's a new problem, but it could be something like this: stackoverflow.com/questions/50808513/… or this: stackoverflow.com/questions/54012067/…

Mithson Over a year ago

the solutions suggested by you for reading data were using maps and I dont want to use maps for just retrieving three fieldvalues is there any other way to do so like creating a future then storing a value inside it and make it accessible outside the future function

Mithson Over a year ago

I just updated this question to include reading part of array-union also now you can suggest me some methods or way to read those three values

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