SequenceGenerator.md

@SequenceGenerator Annotation

The @SequenceGenerator Specifies a sequence generator for generating values for annotated fields marked with @GeneratedValue annotation using the GenerationType.SEQUENCE strategy. This annotation is typically applied to a field, method, or class within a Java class that represents an entity in a data store.

Attributes

1. name (Required): Defines the name of the generator. Bibernate matches @SequenceGenerator with @GeneratedValue which have the same generator parameter as sequence generator name.

2. sequenceName (Required): Specifies the name of the database sequence to be used.

3. initialValue (Optional): Specifies the initial value for the sequence. The default is 1.

4. allocationSize (Optional): Specifies the size of the allocation block for the sequence. The default is 50.

Usage

@Entity
@Table(name = "persons")
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_GENERATOR_PERSON")
    @SequenceGenerator(name = "SEQ_GENERATOR_PERSON", sequenceName = "person_id_custom_seq", initialValue = 5, allocationSize = 5)
    @Column(name = "id")
    private Long id;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;
}

In the example above we specified the name of the generator in the @GeneratedValue annotation, and it matches the name attribute in the @SequenceGenerator annotation. initialValue and allocationSize mean that our sequence will start from 5 and to generate the next 5 identifiers only one query will be made to the database.