I’m have been trying to get all data of collection a and subcollection b and insert them into a List of model to use that list later to show data in a ListView builder , problems are:

1- I can’t get any data in await col.get(); ( it keeps showing out of memory error so I used await col.limit(20).get() and it shows 20 data normally)

2- I can’t insert data into that list, it gives me this error :

A value of type 'allReport' can't be assigned to a variable of type 'List<allReport>'

Try changing the type of the variable, or casting the right-hand type to 'List<allReport>'.

This is my code

Future<List<allReport>> updateAlldocs() async {
  var col = await _firestore.collectionGroup('visits');

  var snapshotChild = await col.limit(20).get(); 

  snapshotChild.docs.map((doc) async {

    var ChildDocument = doc;

    var snapshot_parent =  await _firestore
        .collection('doctors')
        .doc(ChildDocument.reference.parent.parent?.id)
        .get();

    print('>>>>>>>>>>>>>>>>>>>>>>>>>>${snapshot_parent.data()}');

    _docReports = allReport.fromJson(
          ChildDocument.data() ,snapshot_parent.data()?['name'] ,doc.reference.parent.parent?.id ?? ''); // here it keeps giving me the errors (2) showed above in the question


   }).toList();

  print('********************** doctoreName: ${_docReports.map((e) => e.doctoreName)}');

  setState(() {
    _filtereddocReports = _docReports;
  });
  return _filtereddocReports;
}

I also tried to assign snapshotChild to _docReports as this:

Future<List<allReport>> updateAlldocs() async {
  var col = await _firestore.collectionGroup('visits');

  var snapshotChild = await col.limit(20).get();

_docReports = snapshotChild.docs.map((doc) async {

    var ChildDocument = doc;

    var snapshot_parent =  await _firestore
        .collection('doctors')
        .doc(ChildDocument.reference.parent.parent?.id)
        .get();

    print('>>>>>>>>>>>>>>>>>>>>>>>>>>${snapshot_parent.data()}');

    allReport.fromJson(
          ChildDocument.data() ,snapshot_parent.data()?['name'] ,doc.reference.parent.parent?.id ?? '');


   }).cast<allReport>().toList();

  print('********************** doctoreName: ${_docReports.map((e) => e.doctoreName)}');
 // result is: (********************** doctoreName: 0)

  setState(() {
    _filtereddocReports = _docReports;
  });
  return _filtereddocReports;
}