apache/druid · error · UnsupportedOperationException

Cannot convert object to long

Error message

Cannot convert object to long

What it means

Runtime type guard in the unnest cursor's column value selector: when the unnested cell value is neither null nor a Number, the selector cannot fulfill a primitive-long read and raises this error. It fires when a query reads an unnested column as LONG while the underlying unnested values are non-numeric (e.g. strings); fix by coercing the values to numbers or using a column accessor matching the actual value type.

Source

Thrown at processing/src/main/java/org/apache/druid/segment/UnnestColumnValueSelectorCursor.java:172

              return 0;
            }
            if (value instanceof Number) {
              return ((Number) value).floatValue();
            }
            throw new UOE("Cannot convert object to float");
          }

          @Override
          public long getLong()
          {
            Object value = getObject();
            if (value == null) {
              return 0;
            }
            if (value instanceof Number) {
              return ((Number) value).longValue();
            }
            throw new UOE("Cannot convert object to long");
          }

          @Override
          public void inspectRuntimeShape(RuntimeShapeInspector inspector)
          {
            columnValueSelector.inspectRuntimeShape(inspector);
          }

          @Override
          public boolean isNull()
          {
            return getObject() == null;
          }

          @Nullable
          @Override
          public Object getObject()
          {

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Cast the unnest source values to numbers before the query
2. Fix the column's ValueType at ingestion so primitive selectors are used
3. Use string/JSON expressions to extract numeric fields instead of long selectors on objects

Object v = selector.getObject();
if (v instanceof Number) { long l = ((Number) v).longValue(); }

static boolean isLongSafe(Object o) { return o == null || o instanceof Number; }

try { long l = selector.getLong(); } catch (UOE e) { /* fallback: parse or skip */ }

When it happens

Trigger: getLong() invoked on the unnest cursor while iterating a column whose elements are objects (e.g. strings, nested structures, complex/metric payloads).

Common situations: LONG aggregations (COUNT-style or longSum) over an unnested column holding strings; mixed-type array columns where some elements are objects.

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

• Cannot convert object to double
• Cannot convert object to float
• Cannot deserialize type[%s] to an RoaringBitmap64Counter:
• Expected a number or an instance of MergingDigest, but recei
• Object is not of a type that can be deserialized to a quanti

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/a977fb63eb219a78. Report an issue: GitHub.