How to Use JPA or Hibernate for Generating Non-Primary Key Column Values Starting from a Custom Number

How can I set up JPA or Hibernate to automatically generate values for a non-primary key column, starting from a number other than one?

In JPA and Hibernate, generating values for non-primary key fields can be achieved using custom strategies. This is particularly useful when you need to ensure that a specific column has values starting from a number other than the default, which typically starts at one.

@Entity
public class MyEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "custom_value")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "custom_generator")
    @SequenceGenerator(name = "custom_generator", sequenceName = "custom_sequence", initialValue = 100)
    private Integer customValue;

    // Getters and setters
}

Causes

• Trying to directly annotate a non-primary key column with auto-generated value strategies without custom handling.
• Lack of knowledge on how to implement custom generators in JPA or Hibernate.

Solutions

• Implement a custom identifier generator to define how the non-primary key values are generated.
• Use JPA's @GeneratedValue annotation with a sequence or table generator setup that specifies a starting point.
• Combine an application-level service that retrieves the next value for the non-primary key from the database before saving the entity.

Mistake: Using the wrong generation strategy for non-primary key fields.

Solution: Make sure to use a strategy compatible with non-primary key fields, such as SEQUENCE or TABLE, along with a corresponding generator.

Mistake: Not configuring the sequence in the database correctly.

Solution: Ensure that the sequence used for generating the non-primary key values is created in the database and matches the generator configuration.