[hibernate-dev] Fix for Using custom types for auto-generated id columns

[Nádaski Dávid]

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 at aquilanet.hu] 
Sent: Wednesday, December 10, 2008 7:23 AM
To: 'hibernate-dev at lists.jboss.org'
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

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