hibernate/hibernate-orm · error · IllegalStateException

Cannot serialize an EntityUniqueKey which represents a non s

Error message

Cannot serialize an EntityUniqueKey which represents a non serializable property value [

What it means

EntityUniqueKey is the persistence-context key for entities referenced through a unique-key property instead of the primary key (e.g. @ManyToOne pointing at a unique non-PK column / legacy property-ref). Before serializing, writeObject() runs checkAbilityToSerialize(), which requires the referenced property value to implement Serializable and otherwise throws IllegalStateException with the offending entityName.uniqueKeyName.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/engine/spi/EntityUniqueKey.java:98

				&& keyType.isEqual( that.key, key );
	}

	@Override
	public String toString() {
		return "EntityUniqueKey" + MessageHelper.infoString( entityName, uniqueKeyName, key );
	}

	private void writeObject(ObjectOutputStream oos) throws IOException {
		checkAbilityToSerialize();
		oos.defaultWriteObject();
	}

	private void checkAbilityToSerialize() {
		// The unique property value represented here may or may not be
		// serializable, so we do an explicit check here in order to generate
		// a better error message
		if ( key != null && !Serializable.class.isAssignableFrom( key.getClass() ) ) {
			throw new IllegalStateException(
					"Cannot serialize an EntityUniqueKey which represents a non " +
							"serializable property value [" + entityName + "." + uniqueKeyName + "]"
			);
		}
	}

	/**
	 * Custom serialization routine used during serialization of a
	 * Session/PersistenceContext for increased performance.
	 *
	 * @param oos The stream to which we should write the serial data.
	 *
	 */
	public void serialize(ObjectOutputStream oos) throws IOException {
		checkAbilityToSerialize();
		oos.writeObject( uniqueKeyName );
		oos.writeObject( entityName );
		oos.writeObject( key );

View on GitHub (pinned to fad1729dce)

Solutions

1. Make the unique-key property's value type implement java.io.Serializable
2. Rework the association to reference the primary key (or a Serializable key) instead of a non-serializable unique property
3. If a custom UserType produces the value, have it return a Serializable representation

Example fix

// before
public class SkuCode {   // used as unique-key property value
    private final String code;
    public SkuCode(String code) { this.code = code; }
}

// after
public class SkuCode implements java.io.Serializable {
    private final String code;
    public SkuCode(String code) { this.code = code; }
    @Serial private void readObjectNoData() {}
}

Object key = /* unique-key property value before triggering loads */ null;
if (key != null && !(key instanceof java.io.Serializable)) {
    throw new IllegalStateException("Unique-key value of type " + key.getClass().getName() + " is not Serializable; cannot passivate session");
}

static boolean isSerializableUniqueKeyValue(Object v) {
    return v == null || v instanceof java.io.Serializable;
}

try (ObjectOutputStream oos = new ObjectOutputStream(out)) {
    oos.writeObject(session);
} catch (IllegalStateException e) {
    if (String.valueOf(e.getMessage()).contains("non serializable property value")) {
        // clear the persistence context or detach entities, then retry serialization
        session.clear();
    } else {
        throw e;
    }
}

When it happens

Trigger: Serializing a Session/PersistenceContext (or a lazy proxy keeping the session) that contains an entity loaded via a unique-key association whose key property value's class does not implement java.io.Serializable; also hit via the custom serialization routine used when a Session is written to a stream.

Common situations: HTTP session passivation with Open Session in View; Spring Session / Wicket serializing a session holding an open persistence context; distributing sessions or proxies to a compute grid or cache; associations keyed by a custom value type or record that was never made Serializable.

Related errors

• Unable to deserialize from cached file [%s]
• Cannot serialize Session while connected
• Blobs may not be accessed after serialization
• Clobs may not be accessed after serialization
• Given entity is not associated with the persistence context

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/cf4336e2de84a297. Report an issue: GitHub.