Flutter & Firestore - How to create a class object from a nested map from Firestore

Question

I am trying to map a firestore document snapshot to a custom object that I have made but am getting this error upon doing so:

E/flutter ( 6555): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: type '(dynamic) => TestMap' is not a subtype of type '(String, dynamic) => MapEntry<dynamic, dynamic>' of 'transform'

From my understanding it has something to do with the way that I am parsing the nested map 'testMap'. Can any Flutter/Firebase/Dart experts out there help me understand what I am doing wrong and how to fix this.

So my data within Firestore looks like this:

The two class objects to parse this data into a usable object like this:

class Categories {
  final String category;
  final String imageurl;
  List testMap = [];

  Categories(this.category, this.imageurl);
  Map<String, dynamic> toMap() => {
        "category": this.category,
        "imageurl": this.imageurl,
        "testMap": this.testMap
      };

  Categories.fromMap(Map<String, dynamic> map)
      : category = map["category"],
        imageurl = map["imageurl"],
        testMap = map["testMap"].map((map) {  // THE ERROR IS HERE (map) 
          return TestMap.fromMap(map);
        }).toList();
}

class TestMap {
  final String v1;
  final String v2;

  TestMap(this.v1, this.v2);

  Map<String, dynamic> toMap() => {
        "v1": this.v1,
        "v2": this.v2,
      };

  TestMap.fromMap(Map<dynamic, dynamic> map)
      : v1 = map["v1"],
        v2 = map["v2"];
}

Finally I get the data from Firestore like this:

  fromFirestore() {

  final FirebaseAuth auth = FirebaseAuth.instance;

  Categories categoryObject;

  CollectionReference categoriesCollection =
      FirebaseFirestore.instance.collection('categories');

  categoriesCollection.doc('categories').get()
      // ignore: missing_return
      .then((docSnapshot) {
    for (var i = 1; i <= docSnapshot.data().length; i++) {
      print(docSnapshot.data()[i.toString()]['testMap'].toString());

      categoryObject = Categories.fromMap(docSnapshot.data()[i.toString()]);
    }
  });
}

I know that firestore maps to Map<String, dynamic> but the error seems to want this subtype of type '(String, dynamic)' instead of Map<String, dynamic> ... perhaps something to do with how my classes are parsing the maps?

Thanks a lot!

Karen · Accepted Answer · 2021-02-24 01:09:11Z

1

You might need to cast to TestMap

 testMap = map["testMap"].map((map) {  // THE ERROR IS HERE (map) 
          return TestMap.fromMap(map);
        }).toList().cast<TestMap>;

answered Feb 24, 2021 at 1:09

Karen

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