JPA @GeneratedValue(strategy=GenerationType.AUTO) does not work on MySQL

Question

I have an entity that is supposed to get an id from the database automatically. I use MySQL so I would expect annotating that @GeneratedValue(strategy=GenerationType.AUTO) would resolve to IDENTITY behind the scenes and NOT SEQUENCE. However, when I try to persist a new entity it fails saying that hibernate_sequence was not found. It obviously use sequence strategy instead of identity.

I have set the dialect in the persistence.xml to: org.hibernate.dialect.MySQL5InnoDBDialect

Hibernate version 4.2.0.CR1

All sources that I read says that it should use identity when connecting to MySQL with auto as strategy.

Answer 1

If you are using the enhanced identifiers:

 properties.put("hibernate.id.new_generator_mappings", "true");

then the SequenceStyleGenerator is used, and since MySQL doesn't support sequences it will fall-back to TABLE generator. That's why it looks for "hibernate_sequence", which is the default sequence table name.

In case you don't use the new generators, then the native generation strategy is used, which will look for:

public Class getNativeIdentifierGeneratorClass() {
    if ( supportsIdentityColumns() ) {
        return IdentityGenerator.class;
    }
    else if ( supportsSequences() ) {
        return SequenceGenerator.class;
    }
    else {
        return TableHiLoGenerator.class;
    }
}

So it chooses from:

• identity
• sequence
• hilo

depending on your current database capabilities.

In this case for MySQL, it will always pick IDENTITY.