type 'List<dynamic>' is not a subtype of type 'List<LocalltemSize>' in type cast

[Alvish0407]

facing error while reading LocalDraftOrderTb data from the database.

• freezed generated
  • LocalDraftOrderItem
  • LocalItemSize
• drift generated
  • typedef LocalDraftOrder = LocalDraftOrderTbData
  • typedef LocalItem = LocalItemTbData

follow the "👉" for error causing lines

• serialising freezed generated LocalDraftOrderItem's list into the drift generated LocalDraftOrderTb table using TypeConverter->LocalDraftOrderItemListTypeConverter

class LocalDraftOrderTb extends Table {
  TextColumn get id => text()();
  TextColumn get customer => text().nullable()();
  DateTimeColumn get date => dateTime().nullable()();
  TextColumn get orderType => text().map(const LocalOrderTypeConverter())();
👉 TextColumn get items => text().map(const LocalDraftOrderItemListTypeConverter())();

  @override
  Set<Column>? get primaryKey => {id};
}

class LocalDraftOrderItemListTypeConverter
    extends TypeConverter<List<LocalDraftOrderItem>, String> {
  const LocalDraftOrderItemListTypeConverter();

  @override
  List<LocalDraftOrderItem> fromSql(String fromDb) {
    return (jsonDecode(fromDb) as List)
👉        .map((e) => LocalDraftOrderItem.fromJson(e as Map<String, dynamic>))
        .toList();
  }

  @override
  String toSql(List<LocalDraftOrderItem> value) {
    return jsonEncode(value.map((e) => e.toJson()).toList());
  }
}

• serialising drift generated LocalItem table into the freezed generated LocalDraftOrderItem model using JsonConverter->LocalItemJsonConverter

@freezed
class LocalDraftOrderItem with _$LocalDraftOrderItem {
  const factory LocalDraftOrderItem({
    required int qty,
    required String id,
    required LocalDraftOrderItemSize? itemSize,
👉    @LocalItemJsonConverter() required LocalItem item,
  }) = _LocalDraftOrderItem;

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

class LocalItemJsonConverter implements JsonConverter<LocalItem, Map<String, dynamic>> {
  const LocalItemJsonConverter();

  @override
  LocalItem fromJson(Map<String, dynamic> json) {
👉    return LocalItem.fromJson(json);
  }

  @override
  Map<String, dynamic> toJson(LocalItem object) {
    return object.toJson();
  }
}

• finally, LocalItemTb table contains the list of freezed generated LocalItemSize which are being serialised using TypeConverter->LocalItemSizesListTypeConverter

class LocalItemTb extends Table {
  TextColumn get id => text().named("name")();
  TextColumn get image => text().nullable()();
  TextColumn get itemName => text()();
  TextColumn get itemGroup => text()();
  RealColumn get rate => real()();
  TextColumn get sizes =>
      text().map(const LocalItemSizesListTypeConverter()).withDefault(const Constant("[]"))();

  @override
  Set<Column>? get primaryKey => {id};
}

class LocalItemSizesListTypeConverter extends TypeConverter<List<LocalItemSize>, String> {
  const LocalItemSizesListTypeConverter();

  @override
  List<LocalItemSize> fromSql(String fromDb) {
    return (jsonDecode(fromDb) as List)
        // type 'List<dynamic>' is not a subtype of type 'List<LocalltemSize>' in type cast
👉        .map((e) => LocalItemSize.fromJson(e as Map<String, dynamic>))
        .toList();
  }

  @override
  String toSql(List<LocalItemSize> value) {
    return jsonEncode(value.map((e) => e.toJson()).toList());
  }
}

• serialisation/saving data to local db works as it should but deserialising List<LocalItemSize> throws error of

type 'List' is not a subtype of type 'List' in type cast

// <------ database.g.dart ------>
factory LocalItemTbData.fromJson(Map<String, dynamic> json,
    {ValueSerializer? serializer}) {
  serializer ??= driftRuntimeOptions.defaultSerializer;
  return LocalItemTbData(
    id: serializer.fromJson<String>(json['name']),
    image: serializer.fromJson<String?>(json['image']),
    itemName: serializer.fromJson<String>(json['item_name']),
    itemGroup: serializer.fromJson<String>(json['item_group']),
    rate: serializer.fromJson<double>(json['rate']),
    // type 'List<dynamic>' is not a subtype of type 'List<LocalltemSize>' in type cast
👉    sizes: serializer.fromJson<List<LocalItemSize>>(json['sizes']),
  );
}

[Alvish0407]

    // type 'List<dynamic>' is not a subtype of type 'List<LocalltemSize>' in type cast
👉    sizes: serializer.fromJson<List<LocalItemSize>>(json['sizes']),
  );

this is the main error causing line

[simolus3]

As mentioned here (arguably not visible enough, I'll improve the docs here), type converters don't apply to the fromJson factory by default.

This can easily be fixed by using the JsonTypeConverter class, which is almost identical but signals to drift that the converter should also be applied when serializing to JSON instead of just for the db <-> Dart translation.

[Alvish0407]

did you mean JsonTypeConverter mixin ?

[Alvish0407]

this worked. Thanks.

- class LocalItemSizesListTypeConverter extends TypeConverter<List<LocalItemSize>, String> {
+ class LocalItemSizesListTypeConverter with JsonTypeConverter<List<LocalItemSize>, String> {

- class LocalItemModifiersListTypeConverter extends TypeConverter<List<LocalItemModifier>, String> {
+ class LocalItemModifiersListTypeConverter with JsonTypeConverter<List<LocalItemModifier>, String> {