java - 将一个实体持久化到另一个实体之后 ~ Netbeans、J2E、bean、EntityManager

Question

我正在使用 Java EE、Glassfish 和 Netbeans 做一个软件工程项目，由于缺乏 java 经验，我遇到了一个问题。

我正在开发一个网站，为用户提供创建一些 Activity 的可能性。

我能够在表事件中保存有关事件的信息(ID、名称、地点、日期、创建者)，现在的问题是填充另一个表日历.该表中只有 3 个属性:ID(自动且按顺序生成)、创建者电子邮件和事件 ID。此calendar 表的目的是收集所有耦合用户事件:事件不仅可以与其创建者耦合，还可以与其受邀的其他用户耦合。

当我尝试持久保存 calendar 表中的数据时，我收到 NullPointerException 因为在 event 表中生成了 ID自动，我认为当我调用 getEventID 方法时，该值仍然是 null。

如何激活 CalendarManager，它只需获取事件的创建者 和 ID 并将它们写入 日历表？

我希望我已经清楚了，这里有一些文件:

EventManager 工作正常:

@Stateless
public class EventManager {

    @PersistenceContext
    public EntityManager em;

    @Inject
    Principal principal;

    public void saveEvent(Event event) {
        em.persist(event);
    }

    public void deleteEvent(Event event) {
        em.remove(event);
    }

}

CalendarEventsManager 很好，但没有收到正确的参数:

@Stateless
public class CalendarEventsManager {

    @PersistenceContext
    public EntityManager cm;

    @Inject
    Principal principal;

    public void saveCalendarEvents(CalendarEvents calendarevents) {
        cm.persist(calendarevents);     
    }

    public void deleteCalendarEvents(CalendarEvents calendarevents) {
        cm.remove(calendarevents);
    }
}

下面是当用户单击“创建事件”时激活的 Bean 中的关键部分:

public String saveEvent() {
    /* obtain the creator's email */
    creator = um.getLoggedUser().getEmail();
    this.event.setCreator(creator);

    /* save information in db event */
    em.saveEvent(event);

    /* save information in db calendar */

    eventid = event.getID();
    this.calendarevents.setUserEmail(creator);
    this.calendarevents.setEventID(eventid);
    cm.saveCalendarEvents(calendarevents);

    /* next page to visualize */
    return "displayEvent";
}

直到 em.saveEvent(event) 一切都很好并且数据库已正确更新，但问题是当我执行 eventid = getID() (getID 在 Event 类中是公开的并且是正确的)。系统无法读取 ID，因为它没有从刚刚更新的数据库中读取。

这里是事件类:

@Entity
@Table(name="event")
public class Event implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private Integer id;
@NotNull(message = "May not be empty")
private String name;
@NotNull(message = "May not be empty")
private String place;
@NotNull(message = "May not be empty")
private String eventdate;
@NotNull(message = "May not be empty")
private String type;
@NotNull(message = "May not be empty")
private String visibility;
/*@NotNull(message = "May not be empty")
private String weather;*/
@NotNull(message = "May not be empty")
private String creator;

public void setID(Integer id){
    this.id = id;
}

public Integer getID() {
    return id;
}

public void setName(Integer id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getPlace() {
    return place;
}

public void setPlace(String place) {
    this.place = place;
}

public String getDate() {
    return eventdate;
}

public void setDate(String eventdate) {
    this.eventdate = eventdate;
}

public String getType() {
    return type;
}

public void setType(String type) {
    this.type = type;
}

public String getVisibility() {
    return visibility;
}

public void setVisibility(String visibility) {
    this.visibility = visibility;
}

/*public String getWeather() {
    return weather;
}

public void setWeather(String weather) {
    this.weather = weather;
}*/

public String getCreator() {
    return creator;
}

public void setCreator(String creator) {
    this.creator = creator;
}

您有解决这个问题的想法吗？我已经阅读过有关 @PostPersist 注释的内容，但我不知道如何正确应用它:(

感谢所有愿意帮助我的人的建议:D

编辑1:错误可能出在 saveEvent() 中的这段代码中:

    this.calendarevents.setUserEmail(creator);
    this.calendarevents.setEventId(eventid);
    System.out.println("event id after get is:   " + this.calendarevents.getUserEmail());
    System.out.println("event id after get is:   " + this.calendarevents.getEventId());
    cm.saveCalendarEvents(calendarevents);

我已经使用 system.out.println 来验证该值，但错误出现在“this.calendarevents”中，因为没有 system.out 的迹象!这里有完整的 Bean!

@Named(value = "createBean")
@RequestScoped
public class CreateEventBean {

@EJB
private EventManager em;
@EJB
private UserManager um;

private Event event;
private String creator;

@EJB
private CalendarEventsManager cm;

private Integer eventid=0;
private CalendarEvents calendarevents;

public CreateEventBean() {
}

public Event getEvent() {
    if (event == null){
        event = new Event();
    }
    return event;
}

public void setEvent(Event event) {
    this.event = event;

}

public CalendarEvents getCalendarEvent() {
    if (calendarevents == null){
        calendarevents = new CalendarEvents();
    }
    return calendarevents;
}

public void setCalendarEvents(CalendarEvents calendarevents) {
    this.calendarevents = calendarevents;

}

public String saveEvent(){
    /*obtain the creator's email*/
    creator=um.getLoggedUser().getEmail();
    this.event.setCreator(creator);

    /*save information in db event*/
    em.saveEvent(event);

    /*save information in db calendar*/
    System.out.println("event id before get is:   " + eventid);
    eventid=event.getId();
    System.out.println("event id after get is:   " + eventid);

    this.calendarevents.setEventId(eventid);
    System.out.println("eventid in calendar could be:   " + this.calendarevents.getEventId());
    this.calendarevents.setUserEmail(creator);
    System.out.println("useremail in calendar could be:   " + this.calendarevents.getUserEmail());

    cm.saveCalendarEvents(calendarevents);



    /*next page to visualize*/
    return "displayEvent";
}

}

我真的没有发现“this.calendarevents.setEventId(eventid);”中的错误即第 80 行，错误是这样的: Caused by: Warning: #{createBean.saveEvent()}: java.lang.NullPointerExceptionjavax.faces.FacesException:#{createBean.saveEvent()}:java.lang.NullPointerException [引起:java.lang.NullPointerException at it.nyquistmeteocal.beans.CreateEventBean.saveEvent(CreateEventBean.java:80)]

这是 CalendarEvents 类:

@Entity
@Table(name="calendarevents")
public class CalendarEvents implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private Integer id;
@NotNull(message = "May not be empty")
private String useremail;
@NotNull(message = "May not be empty")
private Integer eventid;


public Integer getId() {
    return id;
}

public void setName(Integer id) {
    this.id = id;
}

public String getUserEmail() {
    return useremail;
}

public void setUserEmail(String useremail) {
    this.useremail = useremail;
}


public Integer getEventId() {
    return eventid;
}

public void setEventId(Integer eventid) {
    this.eventid = eventid;
}


}

Answer 1

问题我已经解决了!!

我只是这样修改了日历事件的声明:

private CalendarEvents calendarevents = new CalendarEvents();

我之前没有这样做，我认为如果calendarevents指向NULL它将执行这部分代码:

public CalendarEvents getCalendarEvent() {
    if (this.calendarevents == null){
        this.calendarevents = new CalendarEvents();
    }
    return this.calendarevents;
}

public void setCalendarEvents(CalendarEvents calendarevents) {
    calendarevents = calendarevents;

}

这是否意味着我不需要最后一部分？ :)