java - spring rest doesn't set a id value in correct order

Question

my api used spring 5 version and product entity has a two many to one relations with productsupplier and category and i have to mention that I use jpa for crud operations. I have no problem for posing a product object with two dependency's but problem happens when i post again another object , the next product id value doesn't start in the correct order and next id is 3 times bigger that the last one like(1,4,7,10) instead of the (1,2,3,4) and this makes a problem when my api is in the production and i was wondering how can i solve it

product

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String name;
    @ManyToOne( cascade = CascadeType.ALL)
    @JoinColumn
    private Category category;
    private int price;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn
    private ProductSupplier productSupplier;

//setters and getters

category

  @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String CategoryName;
@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL,mappedBy = "category")
@JsonBackReference
private List<Product> products;
//setters and getters

productSuplier

 @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String name;
    @JsonBackReference
    @OneToMany(mappedBy="productSupplier",fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private List<Product> product;
//setters and getters

post method

 @PostMapping
    @ResponseStatus(HttpStatus.ACCEPTED)
    public ResponseEntity<Product> postProduct(@RequestBody Product product){
        productRepository.save(product);
       return ResponseEntity.ok(product) ;
    }

2 objects that i posted

[
    {
        "id": 1,
        "name": " micro type charger",
        "category": {
            "id": 2,
            "categoryName": "phone"
        },
        "price": 0,
        "productSupplier": {
            "id": 3,
            "name": "samsung"
        }
    },
    {
        "id": 4, //id of new product must be 2 not 4
        "name": " micro type charger",
        "category": {
            "id": 5,
            "categoryName": "phone"
        },
        "price": 0,
        "productSupplier": {
            "id": 6,
            "name": "samsung"
        }
    }

question from:https://stackoverflow.com/questions/65890288/spring-rest-doesnt-set-a-id-value-in-correct-order

Answer 1

Hibernate uses its default db sequence to generate primary key values, if you don't provide any custom sequence name from your database.

In your case, Hibernate using its default db sequence because you didn't provide any custom sequence name. Whenever you're persisting a new product object in the database, two more objects of category and productSupplier are also getting persisted parallely. That's why, id generated for product is 1, then id for category will be generated as 2 and id for productSupplier will be generated as 3.

And When you're persisiting 2nd product object, counter of hibernate sequence is at 4 now. Hence, its showing 4 instead of 2.