apache/flink · error · InvalidFieldReferenceException

Wildcard expressions are not allowed here.

Error message

Wildcard expressions are not allowed here.

What it means

Thrown by PojoTypeInfo.getTypeAt(String) when the fieldExpression is a wildcard character ('*' or '_'). getTypeAt returns the TypeInformation of exactly one field, so a wildcard that selects all fields is semantically invalid here. This is an InvalidFieldReferenceException.

Source

Thrown at flink-core/src/main/java/org/apache/flink/api/java/typeutils/PojoTypeInfo.java:248

                        "Nested field expression \""
                                + tail
                                + "\" not possible on atomic type "
                                + fieldType
                                + ".");
            }
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    @PublicEvolving
    public <X> TypeInformation<X> getTypeAt(String fieldExpression) {

        Matcher matcher = PATTERN_NESTED_FIELDS.matcher(fieldExpression);
        if (!matcher.matches()) {
            if (fieldExpression.startsWith(ExpressionKeys.SELECT_ALL_CHAR)
                    || fieldExpression.startsWith(ExpressionKeys.SELECT_ALL_CHAR_SCALA)) {
                throw new InvalidFieldReferenceException(
                        "Wildcard expressions are not allowed here.");
            } else {
                throw new InvalidFieldReferenceException(
                        "Invalid format of POJO field expression \"" + fieldExpression + "\".");
            }
        }

        String field = matcher.group(1);
        // get field
        int fieldPos = -1;
        TypeInformation<?> fieldType = null;
        for (int i = 0; i < fields.length; i++) {
            if (fields[i].getField().getName().equals(field)) {
                fieldPos = i;
                fieldType = fields[i].getTypeInformation();
                break;
            }
        }

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Do not pass '*' or '_' to getTypeAt — use getFlatFields instead if you need all fields.
2. If calling getTypeAt programmatically, filter out wildcard expressions before the call.

Example fix

// before
pojoTypeInfo.getTypeAt("*");
// after
pojoTypeInfo.getFlatFields("*");

void safeGetTypeAt(CompositeType<?> type, String expr) {
    if ("*".equals(expr) || "_".equals(expr)) {
        throw new IllegalArgumentException(
            "Use getFlatFields for wildcard expressions, not getTypeAt");
    }
    type.getTypeAt(expr);
}

When it happens

Trigger: Calling pojoTypeInfo.getTypeAt("*") or pojoTypeInfo.getTypeAt("_"). ExpressionKeys calls getTypeAt internally at Keys.java:338 only after stripping wildcards, so end users rarely hit this directly — it indicates direct API misuse or a custom wrapper that forwards wildcard expressions.

Common situations: Programmatic code that passes the same expression list to both getFlatFields (which accepts '*') and getTypeAt (which does not). Rarely seen in typical DataStream/DataSet programs.

Related errors

• Invalid format of POJO field expression "{}".
• Wildcard expressions are not allowed here.
• Invalid POJO field reference "{}".
• Unable to find field "{}" in type {}.
• Nested field expression "{}" not possible on atomic type {}.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/e8a51290d80a9f27. Report an issue: GitHub.