java - Hibernate 标准结果会在单个事务期间更新而无需 session 刷新吗？

Question

无论出于何种原因，我有一个代码本质上执行如下所示的操作:它在单个事务/ session 中加载实例几次:

@Transactional
public void fun(final String someName){
    for(int i=0; i<10; ++i) {
        SomeClass someClass = (SomeClass) session()
                    .createCriteria(SomeClass.class)
                    .add(Restrictions.eq("name", someName))
                    .uniqueResult();

        // when not found
        if(someClass == null){
           someClass = new SomeClass();
           someClass.setName(someName); // it SHOULD be found in subsequent criteria calls
       }

        process(someClass);

        session().saveOrUpdate(someClass);
        // session.flush();                     // should it be here?
    }
}

我不确定的是 session().createCriteria... 调用的结果是否在循环期间发生变化。

它在事务中，如果我找不到实体 - 我会创建它(但仅一次)。

那么在第二遍期间，someClass 实例是否始终为非空？

Answer 1

当然你不必调用flush，你应该很少执行flush。然而，证明某些事情的最好方法是使用一个简单的演示，因此我编写了一个 Spring Boot/Data 示例并将其推送到 Github 。该代码与您的代码等效，并使用 Hibernate 4.3.5:

@Transactional
public void createOrUpdateEmployee(String firstName, String lastName) {
  for (int i = 0; i < 10; i++) {
    Employee employee = repository.findByLastName(lastName);
    if (employee == null) {
      employee = new Employee(firstName, lastName);
      if (i > 0) {
        throw new IllegalStateException("This can never happen!");
      }
    }

    log.info(employee);

    repository.save(employee);
  }
}

输出为:

....350  ...EmployeeService      : Employee [id=0, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....396  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....401  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....403  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....405  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....407  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....410  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....412  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....427  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]
....429  ...EmployeeService      : Employee [id=1, firstName=Andreas, lastName=Kluth, hashCode=1686333223]

正如我所期望的，该实体是从 L1 缓存中检索的(hashCode 保持不变)并自动刷新，正如已经提到的文档链接指出的那样:https://access.redhat.com/documentation/en-US/JBoss_Enterprise_Web_Platform/5/html/Hibernate_Core_Reference_Guide/objectstate-flushing.html