`Unhandled Exception: Invalid argument: Instance of '_$_Category'` While sending data to firestore form a freezed generated class

Question

I created two model classes with freezed. One class is having parameter of other class inside it. The problem started when I try to send data to firestore. This following error appears.

E/flutter ( 6175): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Invalid argument: Instance of '_$_Category'
E/flutter ( 6175): #0      convertPlatformException
package:cloud_firestore_platform_interface/…/utils/exception.dart:14
E/flutter ( 6175): #1      MethodChannelDocumentReference.set
package:cloud_firestore_platform_interface/…/method_channel/method_channel_document_reference.dart:44
E/flutter ( 6175): <asynchronous suspension>
E/flutter ( 6175): #2      _JsonCollectionReference.add
package:cloud_firestore/src/collection_reference.dart:109
E/flutter ( 6175): <asynchronous suspension>
E/flutter ( 6175): #3      _WithConverterCollectionReference.add
package:cloud_firestore/src/collection_reference.dart:180
E/flutter ( 6175): <asynchronous suspension>
E/flutter ( 6175): #4      _HomeScreenState.product
package:mr_grocery/home/home_screen.dart:45
E/flutter ( 6175): <asynchronous suspension>

Model classes

1. Product (which has parameter of Category class)

@freezed
class Product with _$Product {
  const factory Product({
    required int amount,
    required List<Category> categories, // Category class generated by freezed
    required String description,
    required List<String> images,
    required bool inStock,
    required String name,
    required String quantity,
    dynamic soldQuantity,
    dynamic createdAt,
    dynamic updatedAt,
    bool? exclusive,
  }) = _Product;

  factory Product.fromJson(Map<String, dynamic> json) =>
      _$ProductFromJson(json);
}

2. Category

@freezed
class Category with _$Category {
  const factory Category({
    required String image,
    required String name,
    // @_ColorSerlizeable() required Color? color,
  }) = _Category;

  factory Category.fromJson(Map<String, dynamic> json) =>
      _$CategoryFromJson(json);
}

Using withConverter from Firestore package

  CollectionReference<Product> products() {
    const path = FirebasePaths.products;
    return _firestore.collection(path).withConverter<Product>(
          fromFirestore: (snapshot, options) => Product.fromJson(
            snapshot.data() ?? const {},
          ),
          toFirestore: (value, options) => value.toJson(),
        );
  }

build.yaml

targets:
  $default:
    builders:
      json_serializable:
        options:
          # Options configure how source code is generated for every
          # `@JsonSerializable`-annotated class in the package.
          #
          # The default value for each is listed.
          any_map: false
          checked: false
          constructor: ""
          create_factory: true
          create_to_json: true
          disallow_unrecognized_keys: false
          explicit_to_json: true // -- Specified to true
          field_rename: none
          generic_argument_factories: false
          ignore_unannotated: false
          include_if_null: true

Allonge

Answer 1

It's behaving like explicit_to_json: false, because of it's trying to encode your class and is not acting with nested toJsons.

On your top-level class its generated toJson should be like:

{
  "myNestedClass": myNestedClass.toJson(),
{

instead of

{
  "myNestedClass": myNestedClass,
{

which causes this crash.

Try to understand why your explicit_to_json: true is not working. You may leave more details so I might help you more assertively.

Are you adding the part 'product.g.dart'; to generate the json_serializable code?

Also, in addition, if you're working with Firebase consider to set any_map: true, since the Firebase struct may have a Map<dynamic, dynamic> instead of only Map<String, Object?>.

Tuition

Yes. I am adding part 'product.g.dart'; file – Allonge