apache/beam · error · IllegalArgumentException

Unsupported field type: " + fieldType

Error message

Unsupported field type: " + fieldType

What it means

convertFromBsonValue's switch over FieldType TypeName has no case for the given field type (e.g. LOGICAL_TYPE, DATETIME, BYTES variants not handled by this helper), so it falls into default and throws. It means the MongoDbIO schema converter does not support converting that FieldType from a BSON value.

Solutions

  1. Change the field to a supported primitive type (STRING, INT64, DOUBLE, BOOLEAN, BYTES as handled) and convert in user code.
  2. Wrap values as STRING (e.g. timestamps as ISO strings) if the connector's converter lacks a case for the logical type.
  3. Upgrade Apache Beam — newer versions may have added support for the FieldType in MongoDbUtils.
  4. Implement a custom schema mapping (DoFn) instead of relying on the connector's automatic conversion.

Example fix

// before
Field.of("createdAt", FieldType.logicalType(new MyInstantLogicalType()))
// after: store as string, parse later
Field.of("createdAt", FieldType.STRING)
Defensive patterns

Strategy: validation

Validate before calling

Set<TypeName> supported = Set.of(TypeName.STRING, TypeName.INT64, TypeName.INT32, TypeName.DOUBLE, TypeName.FLOAT, TypeName.BOOLEAN, TypeName.BYTES, TypeName.ARRAY, TypeName.ITERABLE, TypeName.MAP, TypeName.ROW);
schema.getFields().forEach(f -> {
  if (!supported.contains(f.getType().getTypeName())) {
    throw new IllegalStateException("Unsupported field type in MongoDbIO schema: " + f.getType());
  }
});

Try / catch

try {
  Row row = toRow(doc, schema);
} catch (IllegalArgumentException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Unsupported field type")) {
    throw new SchemaConfigurationException("Use only types supported by MongoDbUtils: " + e.getMessage());
  }
  throw e;
}

Prevention

When it happens

Trigger: A schema field uses a FieldType whose TypeName is not among the handled primitives/collection/MAP/ROW cases — e.g. custom logical types, portable bytes, or unsupported logical types like instant/decimal depending on version — while reading documents via toRow.

Common situations: Custom logical types added by user code; schema inferred from Java types that map to unhandled Beam logical types; Beam version differences where new FieldTypes (e.g. new logical types) postdate the connector's converter.

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/c498124f95a48184. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/io/mongodb/src/main/java/org/apache/beam/sdk/io/mongodb/MongoDbUtils.java:202

          rowMap.put(
              String.valueOf(entry.getKey()), convertFromBsonValue(entry.getValue(), valueType));
        }
        return rowMap;
      case ROW:
        Schema rowSchema = fieldType.getRowSchema();
        if (rowSchema == null) {
          throw new IllegalArgumentException("Row schema cannot be null for type: " + fieldType);
        }
        if (value instanceof Map) {
          return toRow((Map<?, ?>) value, rowSchema);
        } else {
          throw new IllegalArgumentException(
              "Cannot convert value of type "
                  + (value != null ? value.getClass().getName() : "null")
                  + " to Row");
        }
      default:
        throw new IllegalArgumentException("Unsupported field type: " + fieldType);
    }
  }
}

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