Firestore: add() does not support _WithConverterDocumentReference

[idkq]

When you .add() new Document and your collection was initiated with .withConverter<Dog>(), you'll get a DocumentReference<Dog> back as expected. Now, if you want to use this reference to add a new second document that references the first doc, it throws and exception.

Unhandled Exception: Invalid argument: Instance of '_WithConverterDocumentReference<Dog>'
#0      convertPlatformException (package:cloud_firestore_platform_interface/src/method_channel/utils/exception.dart:13:5)
#1      MethodChannelDocumentReference.set (package:cloud_firestore_platform_interface/src/method_channel/method_channel_document_reference.dart:43:13)
<asynchronous suspension>
#2      _JsonCollectionReference.add (package:cloud_firestore/src/collection_reference.dart:108:5)
<asynchronous suspension>
#3      _WithConverterCollectionReference.add (package:cloud_firestore/src/collection_reference.dart:179:22)
<asynchronous suspension>

Why? Because it expects a _JsonDocumentReference instead of a _WithConverterDocumentReference.

The solution is to get the document again from Firestore, but this time without the converter, and use the reference to add a new document.

There must be a better way to do this either by accessing _originalDocumentReference or having the add() method handling this automatically.

[rrousselGit]

Do you have some code samples to reproduce the issue?

[idkq]

Future<void> callThis() async {
    final modelsRef =
        FirebaseFirestore.instance.collection('models').withConverter<Model>(
              fromFirestore: (snapshot, _) => Model.fromJson(snapshot.data()!),
              toFirestore: (model, _) => model.toJson(),
            );

    final myDocRef = await modelsRef.add(Model());

    // Not allowed
    await modelsRef.add(Model(parent: myDocRef));
  }

class Model {
  final DocumentReference? parent;

  Model({this.parent});

  Model.fromJson(Map<String, dynamic> data) : parent = data["parent"];

  Map<String, dynamic> toJson() {
    return {"parent": parent};
  }
}

[rrousselGit]

This is not how withConverter works. You cannot have toJson return a Map that contains a DocumentReference. Nor will data['parent'] will be a DocumentReference either

Maybe you want to do:

class Model {
  Model({required this.property});

  Model.fromJson(Map<String, dynamic> data) : property = data['property'];

  final String property;

  Map<String, dynamic> toJson() {
    return {'property': property};
  }
}

[idkq]

I guess you are confused with the example because of the variable parent.

You cannot have toJson return a Map that contains a DocumentReference. Nor will data['parent'] will be a DocumentReference either

This is not what is expected here. I'm simply trying to add a new document and get a DocumentReference of the document added.

var x = collection.add(Model())

How can I use x as a DocumentReference in any other document, is the question. Think of it as a foreign key of two documents.