Question

为什么我总是得到实体ID的负值？它与increment金额值有关吗？例如，当我使用

时

create sequence message_sequence start 1 increment 1;

我总是得到负值（-38，-44，-45）。但是如果我放

create sequence message_sequence start 1 increment 50;

一切都很好（52,102）。为什么这么奇怪的行为？这是一个实体：

@Entity
@Table(name = "messages")
public class Message {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "message_sequence")
    @SequenceGenerator(name = "message_sequence", sequenceName = "message_sequence")
    private long id;

    private String text;

    public void setText(String text) {
        this.text = text;
    }

    public String getText() {
        return text;
    }
}

程序入口点：

EntityManagerFactory emf = JPAUtility.getEntityManagerFactory();

EntityManager entityManager = emf.createEntityManager();

entityManager.getTransaction().begin();

Message m = new Message();
m.setText("Hello World");

etityManager.persist(m);

entityManager.getTransaction().commit();
entityManager.close();

Answer 1

SequenceGenerator批注中有一个名为allocationSize的变量。默认情况下，此大小为50。这意味着Hibernate将保留50个id，并且不需要为每个插入都检索新的id。设置allocationSize = 1可以解决此问题，以产生新的价值。

Answer 2

将 sqlcmd -S $DB_HOST -U $DB_USER -P $DB_PASSWORD -o $mssqlresult -s "," -W -h -1 -Q "SET NOCOUNT ON SELECT \ TRANS_TYPE AS "ACTION TYPE",\ ORDER_ID AS "ORDER ID",\ EXEC_ID AS "EXECUTION ID",\ ACC_ID AS "ACCOUNT ID",\ TRAD_ID AS "TRADER ID",\ DIRECTION AS "SIDE",\ PP AS "PRICE",\ QUANT AS "QUANTITY",\ UDATE AS "UTC DATE TIME",\ LDATE AS "LOCAL DATE TIME"\ FROM [CDB].[CDS].[V_DART_TRANS]\ WHERE CAST(UDATE AS DATE)='$trade_date'; 代码添加到 allocationSize = 1 后工作正常！

使用GenerationType.SEQUENCE生成负Id值

2 个答案: