如何从 Firestore 集合中删除嵌套属性

Question

I am learning how to use "Firestore" with BLoC pattern in Flutter. I am following this tutorial by Sagar Suri. https://medium.com/codechai/when-firebase-meets-bloc-pattern-fb5c405597e0 . However, this tutorial is old and I am trying to remove bugs and update it for learning purpose. I am facing 2 issue in it. First issue is related with 'updateGoal' function. In example, he copied goals value from collection, cast it into the String and then updated the value. I am getting an error here. Anybody can help me, how I can extract goals value from users, copy into Map, cast it and then update. . This is what I am trying to do.

Future<void> uploadGoal(String title, String documentId, String goal) async {
    DocumentSnapshot doc =
    await _firestore.collection("users").doc(documentId).get();
    Map<String, String> data = doc.data()! as Map<String, String>;
    /****/
    //Getting error here "The operator '[]' isn't defined for the type 'Object? Function()'."
    Map<String, String> goals = doc.data["goals"] != null
         ? doc.data["goals"].cast<String, String>()
         : null;
    /****/
    if (data != null) {
      data[title] = goal;
    } else {
      data = Map();
      data[title] = goal;
    }
    return _firestore
        .collection("users")
        .doc(documentId)
        .set({'goals': data, 'goalAdded': true},  SetOptions(merge: true));
  }

Similar issue, I am facing in removeGoal function.

void removeGoal(String title, String documentId) async {
    DocumentSnapshot doc =
    await _firestore.collection("users").doc(documentId).get();
    Map<String, String> data = doc.data()! as Map<String, String>;
    //How to remove goals title from collection here
    goals.remove(title);
    if (goals.isNotEmpty) {
      _firestore
          .collection("users")
          .doc(documentId)
          .update({"goals": goals});
    } else {
      _firestore
          .collection("users")
          .doc(documentId)
          .update({'goals': FieldValue.delete(), 'goalAdded': false});
    }
  }

Anybody can help me? Thanks.

Answer 1

This looks wrong:

Map<String, String> data = doc.data()! as Map<String, String>;

While all the keys in your document are strings, the goals value is an object/dictionary instead of a string. So at best you can cast it to:

Map<String, dynamic> data = doc.data()! as Map<String, dynamic>;

Once you do that, the statement you commented out to get the goals field should work, but it it doesn't: provide an updated in to your question with the updated code, and the exact error message and stack trace you get.