Hi, So in response to my previous mail, I’ve applied a short fix for IdentifierGeneratorFactory to enable custom types to be used for auto-generated keys. Here’s IdentifierGeneratorFactory’s modified public static Serializable get(….) method, which was extended based on the 3.3.1.GA release: public static Serializable get(ResultSet rs, Type type) throws SQLException, IdentifierGenerationException { Class clazz = type.getReturnedClass(); if ( clazz == Long.class ) { return new Long( rs.getLong( 1 ) ); } else if ( clazz == Integer.class ) { return new Integer( rs.getInt( 1 ) ); } else if ( clazz == Short.class ) { return new Short( rs.getShort( 1 ) ); } else if ( clazz == String.class ) { return rs.getString( 1 ); } else { // try to instantiate the custom type through reflection try { Constructor<?>[] constructors = type.getReturnedClass().getConstructors(); for (Constructor<?> constructor : constructors) { Class<?>[] parameterTypes = constructor.getParameterTypes(); if (parameterTypes.length == 1) if (Long.class.equals(parameterTypes[0])) return (Serializable) constructor.newInstance(rs.getLong(1)); else if (Integer.class.equals(parameterTypes[0])) return (Serializable) constructor.newInstance(rs.getInt(1)); else if (Short.class.equals(parameterTypes[0])) return (Serializable) constructor.newInstance(rs.getShort(1)); else if (String.class.equals(parameterTypes[0])) return (Serializable) constructor.newInstance(rs.getString(1)); } } catch (Throwable t) { throw new IdentifierGenerationException( "Error instantiating custom type: " + type + " with value class: " + type.getReturnedClass(), t ); } throw new IdentifierGenerationException( "Supplied custom type doesn't have a 1-argument constructor which could take either long, integer, short or string: " + type.getReturnedClass().getName() ); } } So this would allow you to use any class for an auto-generated ID, for example: public class UniqueInteger implements Serializable { private Integer internal; public UniqueInteger() { } public UniqueInteger(Integer internal) { this.internal = internal; } } The only requirement is that it should have a 1-argument constructor that can take either long, integer, short or string. Which I think makes sense. Please submit your feedback and thoughts on this! --Dávid _____ From: Nádaski Dávid [mailto:david@aquilanet.hu] Sent: Wednesday, December 10, 2008 7:23 AM To: &#39;hibernate-dev(a)lists.jboss.org&#39; Subject: Using custom types for auto-generated id columns Hi, I was trying to use a custom type for which there was a valid Type implementation, and have run into the following error: 28240 [http-8080-1] ERROR org.hibernate.event.def.AbstractFlushingEventListener - Could not synchronize database state with session org.hibernate.id.IdentifierGenerationException: this id generator generates long, integer, short or string at org.hibernate.id.IdentifierGeneratorFactory.get(IdentifierGeneratorFactory.j ava:116) etc. I’m using MySQL. Looking at the source, it seems like Hibernate doesn’t support anything other than a “long, integer, short or string”. In the parameters of IdentifierGeneratorFactory.get(….), there’s one called “Type type”. This gets mapped correctly to my custom, but since that’s none of those “primitive” types, I get the error – but since the Type information is available, it could easily be used to map say a String using Type.nullSafeGet(ResultSet rs, String[] names, SessionImplementor session, Object owner), since we have both the ResultSet and the Type parameter available in IdentifierGeneratorFactory.get(ResultSet rs, Type type). So then, the proper custom type could be returned if it indeed supports this kind of mapping (which is by definition it’s job). So I propose a patch should be made to IdentifierGeneratorFactory that would enable the use of custom types for identity-generated columns. It’s possible that I’m missing something, in that case please point out my error. Upon request, I think I can supply the appropriate patch, although it seems easy to code. Thanks, David