apache/cassandra · error · MarshalException

Expected a double value, but got a %s: %s

Error message

Expected a double value, but got a %s: %s

What it means

DoubleType.fromJSONObject() accepts either a JSON string (parsed via fromString) or a JSON number (converted with ((Number) parsed).doubleValue()). If the parsed JSON value is neither a String nor a Number (e.g. a boolean, object, array, or null), the ClassCastException is caught and a MarshalException is thrown naming the actual runtime type. This enforces that JSON inputs for double columns are numeric or numeric strings.

Source

Thrown at src/java/org/apache/cassandra/db/marshal/DoubleType.java:108

      catch (NumberFormatException e1)
      {
          throw new MarshalException(String.format("Unable to make double from '%s'", source), e1);
      }
    }

    @Override
    public Term fromJSONObject(Object parsed) throws MarshalException
    {
        try
        {
            if (parsed instanceof String)
                return new Constants.Value(fromString((String) parsed));
            else
                return new Constants.Value(getSerializer().serialize(((Number) parsed).doubleValue()));
        }
        catch (ClassCastException exc)
        {
            throw new MarshalException(String.format(
                    "Expected a double value, but got a %s: %s", parsed.getClass().getSimpleName(), parsed));
        }
    }

    @Override
    public String toJSONString(ByteBuffer buffer, ProtocolVersion protocolVersion)
    {
        Double value = getSerializer().deserialize(buffer);
        if (value == null)
            return "\"\"";
        // JSON does not support NaN, Infinity and -Infinity values. Most of the parser convert them into null.
        if (value.isNaN() || value.isInfinite())
            return "null";
        return value.toString();
    }

    public CQL3Type asCQL3Type()
    {

View on GitHub (pinned to 88fd0f6a0e)

Solutions

  1. Send a JSON number (e.g. 3.14) for double columns in JSON payloads
  2. If sending a string, ensure it is a valid double literal string like "3.14"
  3. Fix the client serializer so the field maps to a numeric JSON type, not boolean/object/null
  4. Use INSERT ... VALUES with typed bind variables instead of JSON when types must be explicit

Example fix

// before
{"score": true}
// after
{"score": 3.14}
Defensive patterns

Strategy: type-guard

Type guard

boolean isDoubleCompatible(Object parsed) { return parsed instanceof Number || (parsed instanceof String && isValidDoubleLiteral((String) parsed)); }

Try / catch

try { term = DoubleType.instance.fromJSONObject(parsed); } catch (MarshalException e) { throw new IllegalArgumentException("Double field must be a JSON number or numeric string", e); }

Prevention

When it happens

Trigger: Posting JSON like {"col": true} or {"col": {"x": 1}} or {"col": null} to a double column through the JSON entry points that call fromJSONObject (e.g. INSERT JSON, fromJSONObject Term construction).

Common situations: Client JSON serializers encode a double column as a boolean or nested object; nulls are not stripped before JSON insert; a schema change turned a formerly-string column into double while payloads stayed unchanged.

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

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/6a342aea8c6b8526. Report an issue: GitHub.