hibernate - how to set auto increment in both mysql and oracle databases?

Question

I'm using hibernate with a MySQL database in my spring MVC project. I have used the @GeneratedValue annotation to set auto-incremenet on my id fields. So all my entities have this piece of code and everything is working as expected:

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

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

At this time, I want to switch to an Oracle database. Now, I have two questions here:

1. What's the best solution to set auto-increment field in oracle? I used this code, but is not working:

@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "id_Sequence")
@SequenceGenerator(name="id_Sequence", allocationSize=1)

2(More important question). Is there any way to use a unique annotation to set auto-increment that will work for both MySQL and Oracle ?

Answer 1

1: If you define your own generator, your have to use the generator attribute in @GeneratedValue . And if you have created your own sequence you have to define the name with sequenceName otherwise hibernate will create one for you.

@SequenceGenerator(name="some_gen", sequenceName="Emp_Seq")
@GeneratedValue(generator="some_gen")

2: The most flexible (and portable) way is to use the TABLE strategy

@GeneratedValue(strategy=GenerationType.TABLE)

or more explicit

@GeneratedValue(generator="some_gen")
@TableGenerator(name="some_gen",
    table="ID_GEN",
    pkColumnName="GEN_NAME",
    valueColumnName="GEN_VAL")

This will generate (if schema generation is enabled) a table ID_GEN with the columns GEN_NAME , GEN_VALUE , if schema generation is not available you have to create this table on your own.

You find more complete information from hibernate docs here: http://docs.jboss.org/hibernate/orm/4.3/manual/en-US/html/ch05.html#mapping-declaration-id-generator