GeneratedValue in Postgres

Question

I have my entity class mapped like below:

@Entity
@Audited
@Table(name=\"messages_locale\")
public class Locale {

    @Id
    @GeneratedValue
    @Getter @S         


        

Answer 1

I think the accepted answer from Petar is not correct, or not correct any longer. The auto-increment in Postgres is handled through SERIAL pseudo type, that’s correct. However, the mapping that Petar gives will result in the following DDL generated by Hibernate 5.1:

CREATE SEQUENCE users_id_seq START 1 INCREMENT 50;

CREATE TABLE … (
    id INT8 NOT NULL,
    …
);

This is not using SERIAL, but a Hibernate managed sequence. It is not owned by the table and no default value has been set. Of course, DDL generation is a feature that many people do not use in production (but many take the generated code as a template).

If you hand-write your DDL and actually used SERIAL, then using GenerationType.SEQUENCE may even conflict with the database behaviour. The correct way to map Hibernate with Postgres’ preferred ID strategy is using GenerationType.IDENTITY. Incidentally, the code is also much shorter and more readable:

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;

Answer 2

In PostgreSQL auto-increment is handled using the SERIAL pseudo type. You use this type when you execute CREATE TABLE.

Now to the point - this SERIAL pseudo type creates a sequence. Autoincrement in PostgreSQL is handled using the created sequence. The default value of the id column becomes - nextval('your_sequence_name').

In Hibernate for an User entity:

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "users_seq_gen")
@SequenceGenerator(name = "users_seq_gen", sequenceName = "users_id_seq")
public Long getId() {
     return id;
}

Read here:

http://www.postgresql.org/docs/8.4/static/datatype-numeric.html#DATATYPE-SERIAL

http://www.neilconway.org/docs/sequences/