apache/beam · error · java.lang.RuntimeException

Aliased enumerations not currently supported.

Error message

Aliased enumerations not currently supported.

What it means

When translating a proto ENUM field into a Beam EnumerationType logical type, the translator builds a name->number map from the enum's values. Protobuf's `allow_alias` option lets two enum value names share the same number; since the Beam enumeration map cannot represent two names for one number, the translator throws a RuntimeException.

Solutions

1. Remove `option allow_alias = true;` from the enum and give each value a distinct number (keep the canonical name, drop the alias).
2. Map the enum field to a plain string/int Beam field instead of EnumerationType (pre-process or use a custom translation).
3. Change the field's type in a wrapper message consumed by Beam so it no longer uses the aliased enum.

Example fix

// before
enum Status {
  option allow_alias = true;
  ACTIVE = 0;
  ENABLED = 0; // alias -> RuntimeException
}
// after
enum Status {
  ACTIVE = 0;
  ENABLED = 1; // distinct numbers
}

// Java: detect aliased enums before schema translation
static boolean hasAliases(Descriptors.EnumDescriptor e) {
  Set<Integer> nums = new HashSet<>();
  for (Descriptors.EnumValueDescriptor v : e.getValues()) {
    if (!nums.add(v.getNumber())) return true;
  }
  return false;
}

try { Schema s = ProtoSchemaTranslator.getSchema(descriptor); } catch (RuntimeException e) { if ("Aliased enumerations not currently supported.".equals(e.getMessage())) { /* fall back to int-typed field or fix proto */ } else throw e; }

When it happens

Trigger: getSchema/beamFieldTypeFromSingularProtoField encounters a proto field whose enum type was declared with `option allow_alias = true;` so at least two EnumValueDescriptors share the same number.

Common situations: Legacy protos using allow_alias for backwards-compatible renames (e.g. OLD_NAME = 1; NEW_NAME = 1); importing shared company protos that use aliases into a Beam pipeline.

Related errors

• Field type not matched.
• Unknown ValueKind
• Unknown ValueKind
• A method marked with SchemaCreate in class
• Any not yet supported

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/69d344c95763289c. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/extensions/protobuf/src/main/java/org/apache/beam/sdk/extensions/protobuf/ProtoSchemaTranslator.java:331

        break;
      case UINT64:
        fieldType = FieldType.logicalType(new UInt64());
        break;
      case SINT64:
        fieldType = FieldType.logicalType(new SInt64());
        break;
      case FIXED64:
        fieldType = FieldType.logicalType(new Fixed64());
        break;
      case SFIXED64:
        fieldType = FieldType.logicalType(new SFixed64());
        break;

      case ENUM:
        Map<String, Integer> enumValues = Maps.newHashMap();
        for (EnumValueDescriptor enumValue : protoFieldDescriptor.getEnumType().getValues()) {
          if (enumValues.putIfAbsent(enumValue.getName(), enumValue.getNumber()) != null) {
            throw new RuntimeException("Aliased enumerations not currently supported.");
          }
        }
        fieldType = FieldType.logicalType(EnumerationType.create(enumValues));
        break;
      case MESSAGE:
      case GROUP:
        String fullName = protoFieldDescriptor.getMessageType().getFullName();
        switch (fullName) {
          case "google.protobuf.Timestamp":
            fieldType = FieldType.logicalType(new NanosInstant());
            break;
          case "google.protobuf.Int32Value":
          case "google.protobuf.UInt32Value":
          case "google.protobuf.Int64Value":
          case "google.protobuf.UInt64Value":
          case "google.protobuf.FloatValue":
          case "google.protobuf.DoubleValue":
          case "google.protobuf.StringValue":

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