GeneratedValue in Postgres

Question

I have my entity class mapped like below:

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

    @Id
    @GeneratedValue
    @Getter @Setter //Project Lombok's annotations, equal to generated getter and setter method
    private int id;
        (...)

I create clean new database ,and properties:

< prop key="hibernate.hbm2ddl.auto" >create < /prop>

WHY THE HELL (Sorry, almost two days wasted on this bug) after created database, i got a sequence in my postgres db?:

CREATE SEQUENCE hibernate_sequence
  INCREMENT 1
  MINVALUE 1
  MAXVALUE 9223372036854775807
  START 2
  CACHE 1;
ALTER TABLE hibernate_sequence
  OWNER TO postgres;

I dont want to have a sequence, I want to have just auto increment auto generated values..

Michael Piefel · Accepted Answer · 2017-02-13 08:56:58Z

29

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;

answered Feb 13, 2017 at 8:56

Michael Piefel

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1 Comment

teik Over a year ago

what database behaviour will conflict when using GenerationType.SEQUENC

Petar Minchev · Accepted Answer · 2012-10-28 09:12:28Z

26

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/

edited Oct 28, 2012 at 9:12

answered Oct 28, 2012 at 8:54

Petar Minchev

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4 Comments

Cichy Over a year ago

is there any way to have sequence that allows to have the same id through other tables? I mean User ID = 1 and Group ID = 1 ?

Petar Minchev Over a year ago

Every id column of every table should have a separate sequence. Look at my edit.

Ola Over a year ago

I guess that generating the sequence in this case will not actually be handled by Postgres, but the Hibernate instead. In the database schema there will not be default value assigned with nextval from a Postgres sequence.

Ola Over a year ago

thorben-janssen.com/jpa-generate-primary-keys

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