java - Spring 启动 hibernate : cannot delete child object separately

Question

我有一个简单的设置，包含两个对象，Event 和 Task，它们作为父子链接，以及用于某些 CRUD 操作的默认 JPA 存储库。我做了一个测试，我将 2 个 Task 附加到一个 Event，然后我尝试对其中一个 调用一个 delete 操作>Task，失败(没有错误，也没有删除)。

如果我在未将 Task 添加到 Event 的情况下运行相同的测试，则操作会成功。我的所有代码都在下面，对我下一步需要做什么有什么想法吗？

@Entity
public class Event {

    @Id
    @GeneratedValue(generator = "hibernate-uuid")
    @GenericGenerator(name = "hibernate-uuid", strategy = "uuid2")
    @Column(unique = true)
    String id;

    String subject;

    @OneToMany(mappedBy="event", cascade = { CascadeType.ALL }, fetch = FetchType.EAGER)
    @JsonIgnoreProperties({"event"})
    List<Task> tasks;
}

@Entity
public class Task {
    @Id
    @GeneratedValue(generator = "hibernate-uuid")
    @GenericGenerator(name = "hibernate-uuid", strategy = "uuid2")
    @Column(unique = true)
    String id;

    String subject;

    @ManyToOne
    @JsonIgnoreProperties({"tasks"})
    Event event;
}

public interface TaskRepository extends JpaRepository<Task, String> {
    public Task findById(String id);
}

和测试:

@Test
public void testSequenceOfActionsOnEventWithSubtasks() {
    // Save a new task
    Task savedTask = given()
            .body(
                    new TaskBuilder()
                            .subject("Previously saved task")
                            .build()
            ).contentType(ContentType.JSON)
            .when().post(TASKS_RESOURCE).as(Task.class);


    Task unsavedTask = new TaskBuilder()
            .subject("Unsaved task")
            .build();


    // Save a new event with an unsaved and a saved task attached
    Event savedEvent = given()
            .body(
                    new EventBuilder()
                            .subject("Main event")
                            .addTask(savedTask)
                            .addTask(unsavedTask)
                            .build()
            ).contentType(ContentType.JSON)
            .when().post(EVENTS_RESOURCE).as(Event.class);


    // Make sure the event now contains two tasks with GUID's attached
    List<Task> tasksForEvent = when().get(EVENT_RESOURCE, savedEvent.getId()).as(Event.class).getTasks();
    assertEquals(2, tasksForEvent.size());

    // Get all tasks, make sure firstTask is in there
    when().get(TASKS_RESOURCE).then().body(SUBJECT_FIELD, hasItems(savedTask.getSubject()));

    // Delete a task that was attached to the event
    when().delete(TASK_RESOURCE, savedTask.getId()).then().statusCode(HttpStatus.SC_OK);

    // Get all tasks, make sure firstTask is NOT in there
    when().get(TASKS_RESOURCE).then().body(SUBJECT_FIELD, not(hasItems(savedTask.getSubject())));

    // Check the event again
    tasksForEvent = when().get(EVENT_RESOURCE, savedEvent.getId()).as(Event.class).getTasks();
    assertEquals(1, tasksForEvent.size());
}

更新:如果我从 Event 类的 @OneToMany 中删除 fetch = FetchType.EAGER，它就可以工作。仍然很高兴知道为什么。下面是我的新 Event 类。

@Entity
public class Event {

    @Id
    @GeneratedValue(generator = "hibernate-uuid")
    @GenericGenerator(name = "hibernate-uuid", strategy = "uuid2")
    @Column(unique = true)
    String id;

    String subject;

    @OneToMany(mappedBy="event", cascade = { CascadeType.ALL })
    @JsonIgnoreProperties({"event"})
    List<Task> tasks;
}

Answer 1

相关摘录自JPA specification :

3.2.4部分:

The semantics of the flush operation, applied to an entity X are as follows:

• If X is a managed entity, it is synchronized to the database.
  • For all entities Y referenced by a relationship from X, if the relationship to Y has been annotated with the cascade element value cascade=PERSIST or cascade=ALL, the persist operation is applied to Y

3.2.2部分:

The semantics of the persist operation, applied to an entity X are as follows:

• If X is a removed entity, it becomes managed.

那么，你的情况是怎样的:

1. 您删除了一个任务。
2. 在事务结束时，Hibernate 将持久化上下文与数据库同步。
3. 它找到Event 实例。它没有变化，但 PERSIST 操作级联到 tasks。
4. PERSIST 应用于 tasks 集合中的所有 Task，包括已删除的，它再次被管理。

要验证这一点，请为 org.hibernate 包启用 TRACE 日志级别，并搜索包含 un-scheduling entity deletion 的消息。

如果延迟加载任务，则不会将PERSIST应用于它们(当然，如果同时未初始化集合)；这就是为什么在这种情况下您看不到这种行为的原因。

解决方案是从 Event 的 tasks 集合中删除已删除的任务，这样 PERSIST 就不会应用于它。