[forge-dev] @GeneratedValue Strategy

[Thomas Frühbeck]

Just for the records, TWIMC :-)

I really was surprised to find this behavior of hibernate generating a 
"hibernate_sequence" on MySQL, where the autoincrement is IMHO the most 
simple and elegant way to create/use a technical primary key - which is 
in the end the reason for the initially desribed behavior of the 
incrementing id from Ryan.
(Similar to the discussion on "Serializeable not getting a default 
serialVersionUID" the question is: should a tool like Forge provide a 
functional core to build on or should it "evangelize" a certain - 
debatable - implementation practice.)

In this case the reason for the discussed behavior is the new 
AnnotationMapping introduced in Hibernate.
See: 5.1.2.2. Identifier generator in 
http://docs.jboss.org/hibernate/orm/3.6/reference/en-US/html/mapping.html

     private static String generatorType(GenerationType generatorEnum, 
Mappings mappings) {
         boolean useNewGeneratorMappings = 
mappings.useNewGeneratorMappings();
         switch ( generatorEnum ) {
             case IDENTITY:
                 return "identity";
             case AUTO:
                 return useNewGeneratorMappings
                         ? 
org.hibernate.id.enhanced.SequenceStyleGenerator.class.getName()
                         : "native";

The old mapping "native" would have been the mapping causing the use of 
"auto_increment", if available.
So there would be two possibilities to react to the issue per default:

     - place a property in persistence.xml:
<property name="hibernate.id.new_generator_mappings" value="false"/>

     - set GenerationType.IDENTITY per default
         thus excluding technically Databases not supporting autoincrement

Unfortunately both are not really attractive :-/

Thomas
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