resolveDataId function Null safety

String? resolveDataId(
  1. {required Map<String, dynamic> data,
  2. required Map<String, TypePolicy> typePolicies,
  3. DataIdResolver? dataIdFromObject}

Returns a unique ID to use to reference this normalized object.

First checks if a TypePolicy exists for the given type. Next, calls the dataIdFromObject function if one is specified. If none is provided, falls back to the 'id' or '_id' field, respectively.

Returns null if this type should not be normalized.


String? resolveDataId({
  required Map<String, dynamic> data,
  required Map<String, TypePolicy> typePolicies,
  DataIdResolver? dataIdFromObject,
}) {
  final typename = data['__typename'];
  if (typename == null) return null;

  final typePolicy = typePolicies[typename];

  if (typePolicy?.keyFields != null) {
    if (typePolicy!.keyFields!.isEmpty) return null;

    try {
      final fields = keyFieldsWithArgs(typePolicy.keyFields!, data);
      return '$typename:${json.encode(fields)}';
    } on MissingKeyFieldException {
      return null;

  if (dataIdFromObject != null) return dataIdFromObject(data);

  final id = data['id'] ?? data['_id'];
  return id == null ? null : '$typename:$id';