java - Hibernate 序列卡在值 41

Question

我的类里面有以下顺序 -

@Entity
public class CustomerOrder {

   @Id
   @SequenceGenerator( name = "CUSTOMER_ORDER_INVOICE_NO_SEQ_NAME", sequenceName = "CUSTOMER_ORDER_INVOICE_NO_SEQ", allocationSize = 20 )
   @GeneratedValue( strategy = GenerationType.SEQUENCE, generator = "CUSTOMER_ORDER_INVOICE_NO_SEQ_NAME" )
   private int id;

   private long orderInvoiceNo;

   //.. getters and setters

}

这是 spring data jpa 存储库类，具有获取 next_val 的方法

  @Repository
  public interface CustomerOrderRepository
    extends CrudRepository<CustomerOrder, Long>, JpaSpecificationExecutor<CustomerOrder> {

     @Query( value = "SELECT next_val FROM CUSTOMER_ORDER_INVOICE_NO_SEQ", nativeQuery = true )
     Long getNextOrderInvoiceNoSeq();
 }

我需要从序列中获取 next_val 并将该值传递到两个不同的位置。因此，我调用存储库的 getNextOrderInvoiceNoSeq() 方法并将该值存储为 orderInvoiceNo -

@Autowired
private CustomerOrderRepository customerOrderRepository;

public void placeCustomerOrder( CustomerOrder customerOrder )
{

 long orderInvoiceNo = customerOrderRepository.getNextOrderInvoiceNoSeq();
 customerOrder.setOrderInvoiceNo(orderInvoiceNo);

 // using the same orderInvoiceNo to my other pojo
 // CustomerPurchase customerPurchase = new CustomerPurchase
 // customerPurchase.setOrderInvoiceNo(orderInvoiceNo);

 //....
 customerOrderRepository.save(customerOrder);
}


 @Entity
 public class CustomerPurchase {

   private String itemId;
   private long orderInvoiceNo;
   //.....     
 }

那么现在放置 customerOrder 的前两次迭代中发生了什么，我得到的 orderInvoiceNo 为 1 和 41，但之后每次我从序列中得到 41 作为 next_val ，因此使每个订单具有相同的发票编号，即41.

Answer 1

MySQL 没有序列，因此在这种情况下 Hibernate 将创建一个表生成器。

Hibernate 将执行 SELECT FOR UPDATE 来获取最新的 next_val 并执行 UPDATE 来增加值:

SELECT next_val as id_val 
FROM CUSTOMER_ORDER_INVOICE_NO_SEQ FOR UPDATE

UPDATE CUSTOMER_ORDER_INVOICE_NO_SEQ 
SET next_val= 2 where next_val=1

getNextOrderInvoiceNoSeq() 仅对最新值执行 SELECT，但不会递增它。

也就是说，我不建议实现它。最好switch to a native sequence并有一个 foreign key客户订单和客户购买。