apache/beam · error · RuntimeException

Unexpected type {}

Error message

Unexpected type {}

What it means

Inside the bytecode-generation helper for selectIntoArrayHelper, the switch over a FieldAccessDescriptor qualifier's FieldType.Kind encountered a kind it has no code-generation branch for. The default arm throws this RuntimeException because only primitive, LIST, MAP, and ROW-like kinds are handled.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/utils/SelectByteBuddyHelpers.java:531

                  fieldId,
                  arrayManager,
                  methodVisitor,
                  implementationContext));

        case MAP:
          return size.aggregate(
              processMap(
                  inputType,
                  fieldAccessDescriptor,
                  qualifiers,
                  qualifierPosition,
                  fieldId,
                  arrayManager,
                  methodVisitor,
                  implementationContext));

        default:
          throw new RuntimeException("Unexpected type " + qualifier.getKind());
      }
    }

    private StackManipulation.Size processList(
        FieldType inputType,
        FieldAccessDescriptor fieldAccessDescriptor,
        List<Qualifier> qualifiers,
        int qualifierPosition,
        int fieldId,
        ArrayManager arrayManager,
        MethodVisitor methodVisitor,
        Context implementationContext) {
      StackManipulation.Size size = new StackManipulation.Size(0, 0);
      FieldType nestedInputType = checkNotNull(inputType.getCollectionElementType());
      Schema nestedSchema = getNestedSchema(nestedInputType, fieldAccessDescriptor);

      // We create temp local variables to store all the arrays we create. Each field in
      // nestedSchema corresponds to a separate array in the output.

View on GitHub (pinned to 12126d8942)

Solutions

  1. Simplify the field selection so nested containers use kinds the generator supports (e.g. select the row field directly instead of diving into the array).
  2. Flatten or convert the data so the array element type is a primitive or row.
  3. Check the Beam version: the set of supported kinds grows over time; upgrade to get more switch cases.
  4. Report/file a Beam issue with the schema and selection expression to get the missing kind case added.

Example fix

// before
PCollection<Row> out = row.apply(Select.fieldNames("events[0].timestamp")); // DATETIME in array -> Unexpected type
// after
// select the whole array, process timestamps after the select
PCollection<Row> out = row.apply(Select.fieldNames("events"));
Defensive patterns

Strategy: validation

Validate before calling

for (Schema.Field f : schema.getFields()) {
  Schema.TypeName t = f.getType().getTypeName();
  if (t == Schema.TypeName.ARRAY || t == Schema.TypeName.ITERABLE) {
    Schema.TypeName el = f.getType().getCollectionElement().getTypeName();
    if (!(el.isPrimitiveType() || el == Schema.TypeName.ROW || el == Schema.TypeName.MAP))
      throw new IllegalArgumentException("Unsupported nested element kind in selection: " + el);
  }
}

Type guard

boolean selectSupported(Schema.Field f) {
  Schema.FieldType t = f.getType();
  switch (t.getTypeName()) {
    case ARRAY: case ITERABLE: {
      Schema.TypeName el = t.getCollectionElement().getTypeName();
      return el.isPrimitiveType() || el == Schema.TypeName.ROW || el == Schema.TypeName.MAP;
    }
    default: return true;
  }
}

Try / catch

try {
  return row.apply(Select.fieldNames(fieldSpec));
} catch (RuntimeException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Unexpected type")) {
    return row.apply(Select.fieldNames(parentField)); // fallback to coarser select
  }
  throw e;
}

Prevention

When it happens

Trigger: Calling selectIntoArrayHelper (through subSelectSize / processList / processMap when generating array element access) with a field whose qualifier type kind is outside the supported set (e.g. unsupported logical/bytes/iterable kind in a nested array selection).

Common situations: Selecting nested array/map elements whose element type is an unusual FieldType (e.g. logical types, DATETIME nested in arrays) that the bytecode selector generator has no case for.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/eca995b81ccf9494. Report an issue: GitHub.