hibernate/hibernate-orm · error · HibernateException

Unknown wrap conversion requested: " +…

Error message

Unknown wrap conversion requested: " + conversionType.getName() + " to " + type.getTypeName()

What it means

AbstractJavaType.unknownWrap is the mirror of unknownUnwrap: JavaType.wrap(value, options) hit a source class the descriptor cannot convert into its represented type. Thrown when a value coming from JDBC (or another source) must be wrapped into the descriptor's Java type and no conversion exists.

Solutions

Broaden the custom JavaType's wrap() to cover the actual incoming classes (Number, String, java.util.Date, ...)
Adjust the native query/addScalar typing so the retrieved class matches what the descriptor wraps
Register/use a converter or a different descriptor that accepts the driver's actual class
Check the dialect/driver version if the incoming class changed after an upgrade

Example fix

// before
@Override
public <X> Money wrap(X value, WrapperOptions options) {
    if (value instanceof String s) return Money.parse(s);
    return unknownWrap(value.getClass()); // driver sends BigDecimal
}
// after
@Override
public <X> Money wrap(X value, WrapperOptions options) {
    if (value instanceof String s) return Money.parse(s);
    if (value instanceof Number n) return Money.of(n);
    return unknownWrap(value.getClass());
}

Defensive patterns

Strategy: type-guard

Validate before calling

// when reading via native query + addScalar, confirm the driver's class is wrap-compatible
Object raw = resultSet.getObject(column);
if (!descriptorWraps(raw.getClass())) {
    raw = resultSet.getString(column); // fall back to a form the descriptor wraps
}

Type guard

// widen and check in a custom JavaType before delegating
static boolean canWrap(Object value) {
    return value == null || value instanceof String || value instanceof Number
        || value instanceof java.util.Date || value instanceof byte[];
}

Try / catch

try {
    return session.createNativeQuery("select amt from t", Money.class).getSingleResult();
} catch (HibernateException e) {
    if (String.valueOf(e.getMessage()).contains("Unknown wrap conversion requested")) {
        // the driver returned a class the descriptor lacks: map as String and parse in a converter
    } else throw e;
}

Prevention

Implement wrap() defensively for Number/String/java.util.Date rather than exact classes
Pin driver versions; test against the real database in CI so wrap targets match driver output
Prefer converters over custom JavaTypes when only domain mapping is needed
Log the incoming class in wrap failure paths for fast diagnosis

When it happens

Trigger: A custom JavaType whose wrap() does not handle the concrete class of the incoming relational value - e.g. the driver returns java.math.BigInteger but the descriptor only wraps Integer; or reading a column through a descriptor registered for a different type.

Common situations: Driver/dialect returning unexpected JDBC classes (Oracle NUMBER as BigInteger, TIMESTAMP as oracle.sql.TIMESTAMP); custom JavaType with partial wrap() coverage; forcing a type on a native query result via addScalar(type) where the underlying value class differs.

Related errors

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/d2d06ef2f621da22. Report an issue: GitHub.

Appendix: source

Thrown at hibernate-core/src/main/java/org/hibernate/type/descriptor/java/AbstractJavaType.java:94

	@Override
	public Comparator<T> getComparator() {
		return comparator;
	}

	@Override
	public String extractLoggableRepresentation(T value) {
		return (value == null) ? "null" : value.toString();
	}

	protected HibernateException unknownUnwrap(Class<?> conversionType) {
		throw new HibernateException(
				"Unknown unwrap conversion requested: " + type.getTypeName() + " to " + conversionType.getName()
		);
	}

	protected HibernateException unknownWrap(Class<?> conversionType) {
		throw new HibernateException(
				"Unknown wrap conversion requested: " + conversionType.getName() + " to " + type.getTypeName()
		);
	}
}

View on GitHub (pinned to fad1729dce)