When using JSONB with BlobColumn nullable, it doesn't accept null

[wtomezaki]

I'm using the new JSONB column, but I want it to be nullable, and it seems that the converter doesn't accept "null"

Also, I'm using the develop branch files which contain the fix #3436

type 'Null' is not a subtype of type 'Uint8List' of 'fromDb'
#0      _DefaultJsonConverter.fromSql (package:drift/src/runtime/types/converters.dart:379:15)

@j.JsonSerializable()
class PropertyArea {
  final String propertyAreaId;
  final GeoJson? mapBoundaries;
  final double area;
  final int areaType;
  final String propertyId;
  final DateTime createdAt;

  PropertyArea(
    this.propertyAreaId,
    this.mapBoundaries,
    this.area,
    this.areaType,
    this.propertyId,
    this.createdAt,
  );

  factory PropertyArea.fromJson(Map<String, dynamic> json) => _$PropertyAreaFromJson(json);

  Map<String, dynamic> toJson() => _$PropertyAreaToJson(this);

  static JsonTypeConverter2<PropertyArea?, Uint8List?, Object?> binaryConverter = TypeConverter.jsonb(
    fromJson: (json) => PropertyArea.fromJson(json as Map<String, Object?>),
    toJson: (pref) => pref?.toJson(),
  );
}

class Properties extends Table {
  TextColumn get propertyId => text()();
  BlobColumn get propertyArea => blob().nullable().map(PropertyArea.binaryConverter)();

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

Even if I try exactly like the documentation using:

  static JsonTypeConverter2<PropertyArea, Uint8List, Object?> binaryConverter = TypeConverter.jsonb(
    fromJson: (json) => PropertyArea.fromJson(json as Map<String, Object?>),
    toJson: (pref) => pref.toJson(),
  );

I get this error in the drift generated file:

The argument type 'JsonTypeConverter2<PropertyArea, Uint8List, Object?>' can't be assigned to the parameter type 'JsonTypeConverter2<PropertyArea, Uint8List, Object>'.

[simolus3]

I will take a look at this example, but the best way to apply type converters to nullable columns is to just make the converter non-nullable, e.g.

  static JsonTypeConverter2<PropertyArea, Uint8List, Object`> binaryConverter = TypeConverter.jsonb(
    fromJson: (json) => PropertyArea.fromJson(json as Map<String, Object?>),
    toJson: (pref) => pref.toJson(),
  );

If drift encounters such a type converter on a nullable column, it will implicitly add the .? and serialize nulls from and to nulls.

[wtomezaki]

I've tried to use it like that, but it still gives me an error:

A value of type 'JsonTypeConverter2<PropertyArea, Uint8List, Object?>' can't be assigned to a variable of type 'JsonTypeConverter2<PropertyArea, Uint8List, Object>'.

The only way drift generates this:

  static JsonTypeConverter2<PropertyArea, Uint8List, Object?>
      $converterpropertyArea = PropertyArea.binaryConverter;
  static JsonTypeConverter2<PropertyArea?, Uint8List?, Object?>
      $converterpropertyArean =
      JsonTypeConverter2.asNullable($converterpropertyArea);

is using it like this:

  static JsonTypeConverter2<PropertyArea, Uint8List, Object?> binaryConverter = TypeConverter.jsonb(
    fromJson: (json) => PropertyArea.fromJson(json as Map<String, Object?>),
    toJson: (pref) => pref.toJson(),
  );

or else it never generates the "asNullable" part. But then it goes back to the error in the generated file

[simolus3]

Sorry, I didn't see that you tried the intended way in the issue description already. That problem should be fixed with 00e65cb.

The reason the first approach doesn't work is essentially a variance issue. TypeConverter.jsonb will always return a converter mapping to a non-nullable blob in SQL. But since Uint8List is a subtype of Uint8List? in Dart, you can assign that converter to an entirely nullable converter and get a runtime error. So the converter always expects an Uint8List but it's possible to make Dart believe that a Uint8List? is fine too.