apache/flink · error · IllegalArgumentException

Unknown field name ' ' for mapping to a row position…

Error message

Unknown field name '%s' for mapping to a row position. Available names are: %s

What it means

In Row's hybrid mode (positionByName != null), setField(String name, value) resolves the name to a position via the positionByName map. When the name is absent, it throws an IllegalArgumentException that helpfully lists all available names (positionByName.keySet()), making typos and schema drift easy to diagnose.

Solutions

  1. Use one of the names printed in the exception message (positionByName.keySet())
  2. Validate the name against row.getFieldNames(true) before writing
  3. Share field-name constants between the code that defines the row and the code that fills it

Example fix

// before
row.setField("userId", 7); // available: [user_id, name]

// after
row.setField("user_id", 7);
Defensive patterns

Strategy: validation

Validate before calling

List<String> names = row.getFieldNames(true);
if (names != null && !names.contains(name)) {
    throw new IllegalArgumentException("Unknown '" + name + "'; available: " + names);
}
row.setField(name, value);

Type guard

static boolean canSetByName(Row row, String name) {
    List<String> names = row.getFieldNames(true);
    return names != null && names.contains(name);
}

Try / catch

catch (IllegalArgumentException e) { // message already lists available names; fix the mapping }

Prevention

When it happens

Trigger: Calling setField(name, value) on a hybrid row where name is not in the attached name list — misspelled, different case, or a field from a newer/older schema.

Common situations: Connector column mappings after upstream renames; configuration-driven field names flowing into row construction; inconsistent casing conventions (camelCase vs snake_case) between producer and consumer.

Related errors

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/907698ec0b21f2ae. Report an issue: GitHub.

Appendix: source

Thrown at flink-core/src/main/java/org/apache/flink/types/Row.java:348

                    "Accessing a field by position is not supported in name-based field mode.");
        }
    }

    /**
     * Sets the field's content using the specified field name.
     *
     * <p>Note: The row must operate in name-based field mode.
     *
     * @param name the name of the field
     * @param value the value to be assigned to the field
     */
    public void setField(String name, @Nullable Object value) {
        if (fieldByName != null) {
            fieldByName.put(name, value);
        } else if (positionByName != null) {
            final Integer pos = positionByName.get(name);
            if (pos == null) {
                throw new IllegalArgumentException(
                        String.format(
                                "Unknown field name '%s' for mapping to a row position. "
                                        + "Available names are: %s",
                                name, positionByName.keySet()));
            }
            assert fieldByPosition != null;
            fieldByPosition[pos] = value;
        } else {
            throw new IllegalArgumentException(
                    "Accessing a field by name is not supported in position-based field mode.");
        }
    }

    /**
     * Returns the set of field names if this row operates in name-based field mode, otherwise null.
     *
     * <p>This method is a helper method for serializers and converters but can also be useful for
     * other row transformations.

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