相关疑难解决方法(0)

我读过大约4级隔离:

Isolation Level       Dirty Read    Nonrepeatable Read  Phantom Read  
READ UNCOMMITTED      Permitted       Permitted           Permitted
READ COMMITTED              --        Permitted           Permitted
REPEATABLE READ             --             --             Permitted
SERIALIZABLE                --             --              --

我想了解每个事务隔离对表的锁定

READ UNCOMMITTED - no lock on table
READ COMMITTED - lock on committed data
REPEATABLE READ - lock on block of sql(which is selected by using select query)
SERIALIZABLE - lock on full table(on which Select query is fired)

下面是事务隔离中可能发生的三种现象
Dirty Read - no lock
Nonrepeatable Read - 没有脏读作为锁定提交数据
Phantom …

更新数据库时我应该更喜欢什么？两种方法的优缺点是什么？何时使用其中一种方法？

public void disemployEmployee(Integer employeeId, Date endDate) {
    Employee employee = (Employee)em.find("Employee", employeeId);
    employee.getPeriod().setEndDate(endDate);
    em.flush();
}

public void disemployEmployee(Integer employeeId, Date endDate) {
    Employee employee = (Employee)em.find("Employee", employeeId);
    em.getTransaction().begin();
    employee.getPeriod().setEndDate(endDate);
    em.getTransaction().commit();
}

MOTHER感谢JPQL查询,我试图删除大量的行.

所述Mother类的定义如下:

@Entity
@Table(name = "MOTHER")
public class Mother implements Serializable {

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "mother", 
               orphanRemoval = true)
    private List<Child> children;    
}

@Entity
@Table(name = "CHILD")
public class Child  implements Serializable {

    @ManyToOne
    @JoinColumn(name = "MOTHER_ID")
    private Mother mother;    
}

如您所见,Mother该类具有"子",并在执行以下查询时:

String deleteQuery = "DELETE FROM MOTHER WHERE some_condition";
entityManager.createQuery(deleteQuery).executeUpdate();

抛出异常:

ERROR - ORA-02292: integrity constraint <constraint name> violated - 
                   child record found

当然,我可以首先选择我要删除的所有对象,然后在迭代它之前将它们检索到列表中以删除所有检索到的对象,但是这样的解决方案的性能会很糟糕!

那么有没有办法利用前面的映射来有效地删除所有Mother对象和Child与它们相关的所有对象,而无需首先为所有子项编写查询？

我的问题是为什么冲洗不起作用:

public void ejbService(){
   Customer c = em.find(Customer.class,1);
   c.setName("newName");
   em.flush();
   //at this point when I query mysql table I can not see "newName"


   thread.sleep(10000);

   c.setName("anotherName");
}

完成方法后,我在db中看到"anotherName",我也用em.find(Customer.class,1,Lock.None)检查它; 但仍然不行

RGDS

我正在尝试使用 hibernate (Spring JPA) 实现以下本机查询逻辑。但是，如果其中一条记录无法持久保存，则 save(Iterable) 会引发异常并回滚整个事务。有什么方法可以捕获记录错误并继续插入其他记录。

例如：-

原生 SQL 查询

set autocommit=false\ndelete from EMPLOYEE;\ninsert into EMPLOYEE(id, name, sal) values(2, \xe2\x80\x98Roy\xe2\x80\x99, \xe2\x80\x98rt\xe2\x80\x99); \xe2\x80\x94-stmt1\ninsert into EMPLOYEE(id, name, sal) values(2, \xe2\x80\x98Joe\xe2\x80\x99, 3000);\ncommit;\n

注意：Sal 列在 EMPLOYEE 表中是数字。即使 stmt1 失败，执行仍会继续。

Hibernate（CrudRepository）

@Autowired\nCrudRepository employeeRepository;\n\n@Transactional\npublic void saveToDB(List dataList) {\n   employeeRepository.deleteAll();\n   employeeRepository.save(dataList);\n}\n