Firestore/Flutter: Iterating through the ID of a collection of documents and output them as a list

Question

I want to write a code that outputs the document id of each document within a document that is in a collection that the StreamBuilder is subscribed to.

My Firestore structure is this:

• 2020-2021 (Collection)
  • MyClass (Document)
    • Scores (Collection)
      • Quiz 1 (these are the document ids of the documents)
      • Quiz 2
      • Quiz 3

My code might seem complicated but what I'm trying to achieve in a nutshell, is to output the document ids of all documents in a collection (Scores) into a list, while the StreamBuilder is subscribed to the changes of the document collecting (MyClass) the collection. However, it gives me this error: NoSuchMethodError: 'doc', method not found, Receiver: null, Arguments:[] I think I'm having a syntax error, but I have no idea how to correct it. I'm also not sure whether the use of the map method is correct.

    classname = "MyClass";
    CollectionReference schoolYear =
      FirebaseFirestore.instance.collection("2020-2021");
    
    Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(30),
      child: StreamBuilder(
        builder: (context, streamSnapshot) {
          return SingleChildScrollView(
            child: DataTable(
              columns: streamSnapshot.data.doc.map((DocumentSnapshot document) {
                return new DataColumn(label: Text(document.id));
              }).toList(),
              rows: <DataRow>[],
            ),
          );
        },
        stream: schoolYear.doc(classname).snapshots(),
      ),
    );
  }

Here's the full error log (after changing to Thavamani's code):

Answer 1

Your current listener schoolYear.doc(classname).snapshots() listen to the changes made on your document MyClass and it doesn't carries it's sub-collection Scores details.

To get all document IDs inside Scores collection, you can have either stream/future that gets all the documents available in the collection.

Ex, stream builder way

Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(30),
      child: StreamBuilder(
        builder: (context, streamSnapshot) {
           if (streamSnapshot.hasError) {
              // print() you could check errors here
              return Icon(
                Icons.error_outline,
                color: Colors.red,
                size: 60,
              );
           } else if (streamSnapshot.hasData) {
               return SingleChildScrollView(
                  child: DataTable(
                  columns: streamSnapshot.data.docs.map((DocumentSnapshot document) {
                  return new DataColumn(label: Text(document.documentID));
                 }).toList(),
                rows: <DataRow>[],
              ),
            );
          } else {
            return SizedBox(
                 child: const CircularProgressIndicator(),
                 width: 60,
                 height: 60,
            );
        }
        stream: schoolYear.doc(classname).collection('Scores').snapshots(),
      ),
    );
  }

• If you don't want to listen to the documents, simply go with future builder using the collection('Scores').getDocuments() instead of collection('Scores').snapshots()