apache/druid · error · ParseException

Could not ingest value [%s] as long for dimension [%s]. A lo

Error message

Could not ingest value [%s] as long for dimension [%s]. A long column cannot have multiple values in the same row.

What it means

convertObjectToLong throws this ParseException when the value is a List: long columns are single-valued, so a multi-value (list) input cannot be converted to long. Druid rejects multi-value rows for numeric columns during ingestion.

Source

Thrown at processing/src/main/java/org/apache/druid/segment/DimensionHandlerUtils.java:422

        }
        throw new ParseException((String) valObj, message);
      }
      return ret;
    } else if (valObj instanceof List) {
      final String message;
      if (objectKey != null) {
        message = StringUtils.nonStrictFormat(
            "Could not ingest value [%s] as long for dimension [%s]. A long column cannot have multiple values in the same row.",
            valObj,
            objectKey
        );
      } else {
        message = StringUtils.nonStrictFormat(
            "Could not ingest value [%s] as long. A long column cannot have multiple values in the same row.",
            valObj
        );
      }
      throw new ParseException(
          valObj.getClass().toString(),
          message
      );
    } else {
      final String message;
      if (objectKey != null) {
        message = StringUtils.nonStrictFormat(
            "Could not convert value [%s] to long for dimension [%s]. Invalid type: [%s]",
            valObj,
            objectKey,
            valObj.getClass()
        );
      } else {
        message = StringUtils.nonStrictFormat(
            valObj.getClass().toString(),
            "Could not convert value [%s] to long. Invalid type: [%s]",
            valObj,
            valObj.getClass()

View on GitHub (pinned to 9b90983fd2)

Solutions

  1. Flatten or unnest the array before ingestion (e.g. use an auto-deny/unfold, or a transform taking the first element).
  2. Ensure the input spec declares the field as a multi-value string dimension instead of long if it's genuinely multi-valued.
  3. Pre-process input so numeric columns are scalars (e.g. take element [0] or join).
  4. Use a transform like "CAST(json_query(...), 'LONG')" or extract a single value deterministically.

Example fix

// before: row has "vals": [10, 20] for long column vals
// after: transform to take the first element
"transforms": [{"type": "expression", "name": "vals", "expression": "CAST(vals[0] AS LONG)"}]
Defensive patterns

Strategy: validation

Validate before calling

boolean isScalar(Object v) {
  return v == null || !(v instanceof List);
}

Type guard

Long firstAsLong(Object v) {
  if (v instanceof List) {
    List<?> l = (List<?>) v;
    return l.isEmpty() ? null : asLong(l.get(0));
  }
  return asLong(v);
}

Try / catch

try {
  return DimensionHandlerUtils.convertObjectToLong(value, fieldName, objectKey);
} catch (ParseException e) {
  if (e.getMessage().contains("multiple values")) {
    log.warn("Dropping multi-valued row for long field [%s]", fieldName);
    return null;
  }
  throw e;
}

Prevention

When it happens

Trigger: A row's value for a long column is a List (multi-value dimension from JSON/Kafka input), and convertObjectToLong is invoked; also hit by convertObjectToType dispatching to convertObjectToLong.

Common situations: Nested/array JSON fields mapped to a long column; flattened event data that occasionally contains multiple values (e.g. "ids": [1,2]); Kafka/JSON input with inconsistent cardinality per row.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/bbf810eb603b5cd1. Report an issue: GitHub.