Manually specify the value of a primary key in JPA @GeneratedValue column

Question

I\'m having an Entity which has a primary key / id field like the following:

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
         


        

Answer 1

Database-centric solution to your problem:

1. Create an auxiliary, nullable column in your table. It will hold your manually assigned ids:

   CREATE TABLE `test_table`
   (
     `id` bigint(20) NOT NULL AUTO_INCREMENT,
     `manual_id` bigint(20) NULL,
     `some_other_field` varchar(200) NOT NULL,
     PRIMARY KEY(id)
   );
   

2. Map this column to a normal field in your Entity:

   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private Long id;
   @Column(name="manual_id")
   private Integer manualId;
   

3. Create a trigger that sets the table id to the manual assigned id if it is not null:

   DELIMITER //
   CREATE TRIGGER `test_table_bi` BEFORE INSERT ON `test_table`
     FOR EACH ROW 
     BEGIN
       IF NEW.`manual_id` IS NOT NULL THEN 
         SET NEW.`id` = NEW.`manual_id`;
       END IF;
   END;//
   DELIMITER;    
   

4. Always use the manualId when you need to assign a custom id. The trigger will do the magic for you:

   testEntiy.setManualId(300);
   entityManager.persist(testEntity);
   

5. After the database import phase, simple remove the trigger, the auxiliary column and it's mapping.

   DROP TRIGGER `test_table_bi`;
   ALTER TABLE `test_table` DROP COLUMN `manual_id`;
   

---

Warning

If you manually specify an id greater than the current AUTO_INCREMENT value, the next generated id will jump to the value of the manually assigned id plus 1, e.g.:

INSERT INTO `test_table` (manual_id, some_other_field) VALUES (50, 'Something');
INSERT INTO `test_table` (manual_id, some_other_field) VALUES (NULL, 'Something else');
INSERT INTO `test_table` (manual_id, some_other_field) VALUES (90, 'Something 2');
INSERT INTO `test_table` (manual_id, some_other_field) VALUES (NULL, 'Something else 2');
INSERT INTO `test_table` (manual_id, some_other_field) VALUES (40, 'Something 3');
INSERT INTO `test_table` (manual_id, some_other_field) VALUES (NULL, 'Something else 3');

Will wield the results:

+----+-----------+------------------+
| id | manual_id | some_other_field |
+----+-----------+------------------+
| 50 |        50 | Something        |
| 51 |      NULL | Something else   |
| 90 |        90 | Something 2      |
| 91 |      NULL | Something else 2 |
| 40 |        40 | Something 3      |
| 92 |      NULL | Something else 3 |
+----+-----------+------------------+

To avoid problems it is highly recommended to set the AUTO_INCREMENT column to start with a number greater than all of the existing ids in your previous database, e.g.:

ALTER TABLE `test_table` AUTO_INCREMENT = 100000;