Flutter JSON serializable using json_annotation package how to use JsonConverter with Firebase Firestore DocumentReference

Question

I'm trying to save a DocumentReference in models using JSON serializable with a custom JsonConverter but not doing it correct

here is my model

@DocumentSerializer()
DocumentReference? recentTrainingRef;

My DocumentSerializer Class

class DocumentSerializer
    implements JsonConverter<DocumentReference, DocumentReference> {
  const DocumentSerializer();

  @override
  DocumentReference fromJson(DocumentReference docRef) => docRef;

  @override
  DocumentReference toJson(DocumentReference docRef) => docRef;
}

I'm getting the following error Could not generate fromJson code for recentTrainingRef.

Solution

As noted in my answer Are type DocumentReference supported by json_serializable?, due to https://github.com/google/json_serializable.dart/issues/822, you need a nullable document serializer because your type (DocumentReference?) is nullable (because of the ? at the end).

Quite simply (and you'll need to add @DocumentSerializerNullable() annotation before the class you're trying to use it with).

class DocumentSerializerNullable
    implements JsonConverter<DocumentReference?, DocumentReference?> {
  const DocumentSerializerNullable();

  @override
  DocumentReference? fromJson(DocumentReference? docRef) => docRef;

  @override
  DocumentReference? toJson(DocumentReference? docRef) => docRef;
}

Comments

[Developer Extraordinare]

I'm assuming that DocumentReference is a Firebase class and if so I'm guessing that it's not generating it because DocumentReference probably doesn't have a toJson.

[Almog]

yea but the whole idea is to save the ref in the backend flutter side - pub.dev/documentation/cloud_firestore/latest/cloud_firestore‌​/… Functions side - updateObject.recentTraining = snap.ref; firebase.google.com/docs/reference/js/v8/…

[Developer Extraordinare]

In that case, you only need the id, right?

[undershock]

@developerextraordinare - you might need the full path (which yes you could pass as a string as well, but I didn't really like the idea of deserializing arbitrary paths from JSON when they're being stored as a first class format). stackoverflow.com/questions/71022764/…