EclipseLink sequential numbered ID's using GenerationType.Identity

Question

Extending this question Why does eclipselink consume the whole allocationSize each time it's rebooted? I would like to know what a proper solution for this problem is, the only answer in that post suggests switching to an IDENTITY strategy which i have done but i cannot see the changes. The allocation size of 50 is still in affect. Does anyone have any examples on how to generate sequential identifiers (1, 2, 3) based on each entity (table) and not a single sequence accessible by all tables?

Answer 1

You have the TableGenerator annotation for that purpose.

@Entity
public class Employee {

    @Id
    @TableGenerator(name="TABLE_GEN", table="SEQUENCE_TABLE", pkColumnName="SEQ_NAME",
        valueColumnName="SEQ_COUNT", pkColumnValue="EMP_SEQ", allocationSize = 500, initialValue = 1)
    @GeneratedValue(strategy=GenerationType.TABLE, generator="TABLE_GEN")
    private long id;
    ...
}

@Entity
    public class PaySlip {

        @Id
        @TableGenerator(name="SECOND_TABLE_GEN", table="SECOND_SEQUENCE_TABLE", pkColumnName="SEQ_NAME",
            valueColumnName="SEQ_COUNT", pkColumnValue="SECOND_EMP_SEQ", allocationSize = 500, initialValue = 1)
        @GeneratedValue(strategy=GenerationType.TABLE, generator="SECOND_TABLE_GEN")
        private long id;
        ...
    }

Make sure that all the name/*table* and pkColumnValue fields value are unique.

Reference

• Sequence Strategies