apache/beam · error · UnsupportedOperationException

Converting YAML type '%s' to '%s' is not supported

Error message

Converting YAML type '%s' to '%s' is not supported

What it means

toBeamValue only knows how to convert a limited set of YAML value types (scalars, lists, maps-to-row) to schema field types; anything else, or a type/field-type pairing with no conversion path, hits the final UnsupportedOperationException with the Java value class and target FieldType in the message.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/utils/YamlUtils.java:148

                          toBeamValue(field.withType(innerType), v, convertNamesToCamelCase)))
              .collect(Collectors.toList());
    }

    if (yamlValue instanceof Map) {
      if (fieldType.getTypeName() == Schema.TypeName.ROW) {
        Schema nestedSchema =
            Preconditions.checkNotNull(
                fieldType.getRowSchema(),
                "Received a YAML '%s' type, but output schema field '%s' does not define a Row Schema",
                yamlValue.getClass(),
                fieldType);
        return toBeamRow((Map<String, Object>) yamlValue, nestedSchema, convertNamesToCamelCase);
      } else if (fieldType.getTypeName() == Schema.TypeName.MAP) {
        return yamlValue;
      }
    }

    throw new UnsupportedOperationException(
        String.format(
            "Converting YAML type '%s' to '%s' is not supported", yamlValue.getClass(), fieldType));
  }

  @SuppressWarnings("nullness")
  public static Row toBeamRow(
      @Nullable Map<String, Object> map, Schema rowSchema, boolean toCamelCase) {
    if (map == null || map.isEmpty()) {
      List<Field> requiredFields =
          rowSchema.getFields().stream()
              .filter(field -> !field.getType().getNullable())
              .collect(Collectors.toList());
      if (requiredFields.isEmpty()) {
        return Row.nullRow(rowSchema);
      } else {
        throw new IllegalArgumentException(
            String.format(
                "Received an empty Map, but output schema contains required fields: %s",

View on GitHub (pinned to 12126d8942)

Solutions

1. Align the YAML value type with the schema field type (e.g. provide a mapping where the schema expects a row).
2. Change the schema field type to match what the YAML actually contains.
3. Pre-convert unsupported YAML types (e.g. timestamps to strings, binary to base64 strings) before calling toBeamRow.
4. Upgrade Beam — YamlUtils gains more conversions over time.
5. Do a manual pre-pass: parse with SnakeYAML yourself and construct the Row field-by-field for exotic types.

Example fix

// before (YAML)
created: 2023-01-01T00:00:00Z // parsed as Date, unsupported target
// after
created: "2023-01-01T00:00:00Z" // string, or declare field as DATETIME supported in newer Beam

Object v = yamlMap.get(fieldName);
Schema.TypeName t = schema.getField(fieldName).getType().getTypeName();
if (v instanceof String && !(t == Schema.TypeName.STRING || t.isNumericType()))
  throw new IllegalArgumentException("Unsupported YAML scalar for " + t);
if (v instanceof Map && !(t == Schema.TypeName.ROW || t == Schema.TypeName.MAP))
  throw new IllegalArgumentException("Mapping not allowed for " + t);
if (v instanceof List && !(t == Schema.TypeName.ARRAY || t == Schema.TypeName.ITERABLE))
  throw new IllegalArgumentException("Sequence not allowed for " + t);

boolean yamlValueMatches(Object v, Schema.FieldType t) {
  if (v == null) return t.getNullable();
  switch (t.getTypeName()) {
    case STRING: return v instanceof String || v instanceof Number || v instanceof Boolean;
    case ROW: case MAP: return v instanceof Map;
    case ARRAY: case ITERABLE: return v instanceof List;
    default: return v instanceof String || v instanceof Number || v instanceof Boolean;
  }
}

try {
  return YamlUtils.toBeamRow(yamlString, schema);
} catch (UnsupportedOperationException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Converting YAML type")) {
    logger.warning("Unsupported YAML conversion: " + e.getMessage());
    return null; // or dead-letter the record
  }
  throw e;
}

When it happens

Trigger: A YAML value's Java runtime type has no conversion for the target FieldType — e.g. a MAP field returns the raw yamlValue unchecked but scalar-to-LOGICAL/BYTES/DATETIME combinations, or a List where the field is not an array/iterable, reach the fall-through throw after the instanceof checks.

Common situations: YAML documents with dates/timestamps parsed into Date objects for DATETIME fields in older versions, binary data for BYTES fields, or mismatched schema (field declared INTEGER but YAML has a nested mapping).

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• The input schema must have exactly one field of type byte.
• FieldType unexpected +fieldType.getTypeName()
• Cannot merge two types: +fieldType1.getTypeName()+ and +fiel
• value type is '%s' for field type '%s'
• Cannot convert between types that don't have equivalent sche

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/33ece89c78c52100. Report an issue: GitHub.