apache/flink · error · IllegalArgumentException

Unknown field name ' ' for mapping to a position.

Error message

Unknown field name '%s' for mapping to a position.

What it means

In Row's hybrid mode (created with positions plus a name-to-position mapping, positionByName != null), getField(String name) looks the name up in positionByName; if the map has no entry for the given string, it throws this IllegalArgumentException listing the unknown name. The row knows its field positions but not the requested label.

Solutions

  1. Use one of the row's actual field names: check row.getFieldNames(true) or the exception's available-names message (setField lists them)
  2. For lookups that may legitimately miss, check containsField-style via getFieldNames before calling getField
  3. Centralize field-name constants instead of scattering string literals

Example fix

// before
Object v = row.getField("userName"); // attached name is "user_name"

// after
Object v = row.getField("user_name");
// or guard:
if (row.getFieldNames(true).contains("userName")) { ... }
Defensive patterns

Strategy: validation

Validate before calling

List<String> names = row.getFieldNames(true);
if (names == null || !names.contains(fieldName)) {
    throw new IllegalArgumentException("Unknown field '" + fieldName + "'; known: " + names);
}
row.getField(fieldName);

Type guard

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

Try / catch

catch (IllegalArgumentException e) { // log available names from e.getMessage(), fix mapping }

Prevention

When it happens

Trigger: Calling getField(name) on a hybrid Row (built with Row.withPosition(...)-style APIs that attach names) where name is not among the attached names — e.g. a typo, case mismatch, or a name from a different schema version.

Common situations: Schema evolution where a field was renamed; connectors mapping external column names to Row fields with slightly different casing; copy-paste of field name strings between classes.

Related errors

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/d7cbb49de05d64cc. Report an issue: GitHub.

Appendix: source

Thrown at flink-core/src/main/java/org/apache/flink/types/Row.java:291

    public <T> T getFieldAs(int pos) {
        return (T) getField(pos);
    }

    /**
     * Returns 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 or null if not set previously
     * @return the field's content
     */
    public @Nullable Object getField(String name) {
        if (fieldByName != null) {
            return fieldByName.get(name);
        } 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 position.", name));
            }
            assert fieldByPosition != null;
            return fieldByPosition[pos];
        } else {
            throw new IllegalArgumentException(
                    "Accessing a field by name is not supported in position-based field mode.");
        }
    }

    /**
     * Returns the field's content using the specified field name.
     *
     * <p>Note: The row must operate in name-based field mode.
     *
     * <p>This method avoids a lot of manual casting in the user implementation.
     *
     * @param name the name of the field, set previously

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