问题:

It turns out that the following example works when using mysql 5.x, however it doesn't when using an oracle 10g database.

Is there a way to define a unique identifier field that is independent of the database technology?

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name="id")
private long id;

I have tested this in hibernate and the following exception occurs only when using Oracle:

org.hibernate.MappingException: Dialect does not support identity key generation

回答1:

Using a database table is a portable way to generate identifiers.

The simplest way to use a table to generate identifiers is to specify TABLE as the generation strategy:

@Id
@GeneratedValue(strategy=GenerationType.TABLE)
@Column(name="id")
private long id;

The provider will create the default table if you're using schema generation; if not, you must specify an existing table:

@TableGenerator(name="InvTab",
    table="ID_GEN",
    pkColumnName="ID_NAME",
    valueColumnName="ID_VAL",
    pkColumnValue="INV_GEN")
@Id 
@GeneratedValue(generator="InvTab")
@Column(name="id")
private long id;

http://www.oracle.com/technology/products/ias/toplink/jpa/howto/id-generation.html#table

回答2:

I have researched using GenerationType.AUTO and it does appear to be the better option. It allows the JPA implementation to choose whatever is best for the data storage system you are using.