What rules for generating identifiers were configured in Hibernate? What rule is used with the AUTO strategy in PostgreSQL?

In Hibernate, various strategies for entity identifier generation can be configured using the @GeneratedValue annotation with the strategy parameter. The main strategies are:

• IDENTITY — the identifier is generated by the database, for example, through auto-increment.
• SEQUENCE — a database sequence is used.
• TABLE — identifiers are generated through a special table.
• AUTO — Hibernate automatically chooses the strategy based on the database dialect.

When using the AUTO strategy in PostgreSQL, Hibernate defaults to using the SEQUENCE strategy, as PostgreSQL supports sequences. This means that a sequence is created and used in the database for identifier generation.

Example:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    // ...
}

In PostgreSQL, this corresponds to using a sequence for generating the id.