实体不能为空？

Question

我想从数据库中检索找到的对象或null。

在我ProjectFollowerImpl，为useFollowingProject我返回如果查询不返回任何结果相匹配的查询，或空单实例的方法。

@Override 
public ProjectFollower userFollowingProject(Integer userId, Integer projectId) { 
    return (ProjectFollower) session.createCriteria(classType) 
      .add(Restrictions.eq("user.id", userId)) 
      .add(Restrictions.eq("project.id", projectId)) 
      .uniqueResult(); 
} 

在挂毯页

然后，我有以下方法：

public ProjectFollower getUserFollowingProject() { 
    return projectFollowerDao.userFollowingProject(loggedInUser.getId(), project.getId()); 
} 

@CommitAfter 
void onActionFromFollowProject() { 
    ProjectFollower pf = getUserFollowingProject(); 
    if (pf != null) { 
     projectFollowerDao.delete(pf.getId()); 
    } else { 
     pf = new ProjectFollower(); 
     pf.setProjectId(project); 
     pf.setUserId(loggedInUser); 
     projectFollowerDao.merge(pf); 
    } 
} 

然而，挂毯抛出空指针异常，堆栈跟踪：

com.rile.issuetracker.pages.Tracker getUserFollowingProject() Tracker.java 75 
com.rile.issuetracker.pages.Tracker advised$onActionFromFollowProject_6d8b9673baf() Tracker.java 80 

那么，为什么它是一个问题返回一个空值的对象？我究竟做错了什么 ？

UPDATE：

public class Tracker { 

@Property 
@SessionState 
private User loggedInUser; 

@Property 
@Inject 
private ProjectDao projectDao; 
@Property 
private Project projectP1, project; 
@Property 
private List<Project> projectList; 
@Property 
@Inject 
private ProjectFollowerDao projectFollowerDao; 

@Property 
@Inject 
private TicketDao ticketDao; 
@Property 
private List<Ticket> ticketList; 
@Property 
private Ticket ticketP1; 
@Property 
@Inject 
private TicketFollowerDao ticketFollowerDao; 

@Property 
private Util util = new Util(); 

public boolean getLoggedIn() { 
    return loggedInUser.getEmail() != null; 
}  

@PageLoaded 
void onPageLoad() { 
    projectList = projectDao.loadAll(); 
    ticketList = ticketDao.loadAll(); 
} 

void onActivate(Integer contextValue) { 
    if (contextValue != null) { 
     project = projectDao.getByID(contextValue); 
    } 
    if (project != null) { 
     List ticketListByProjectID = ticketDao.getTicketsByProjectID(project.getId()); 
     if (!ticketListByProjectID.isEmpty()) { 
      ticketList = ticketListByProjectID; 
     } else { 
      ticketList = null; 
     } 
    } 
} 

public ProjectFollower getUserFollowingProject() { 
     return projectFollowerDao.userFollowingProject(loggedInUser.getId(), project.getId());   

} 

@CommitAfter 
void onActionFromFollowProject() { 
    ProjectFollower pf = getUserFollowingProject(); 
    if (pf != null) { 
     projectFollowerDao.delete(pf.getId()); 
    } else { 
     pf = new ProjectFollower(); 
     pf.setProjectId(project); 
     pf.setUserId(loggedInUser); 
     projectFollowerDao.merge(pf); 
    } 
} 

public boolean getIsUserFollowingTicket() { 
    return ticketFollowerDao.isUserFollowingTicket(loggedInUser.getId(), ticketP1.getId()); 
} 

@CommitAfter 
void onActionFromFollowTicket() {} 

public String getActiveFor(String parameter) { 
    if (parameter == null || parameter.isEmpty()) { 
     return null; 
    } 
    switch (parameter) { 
     case "userFollowingProject": 
      return getUserFollowingProject() != null ? "active" : "null"; 
     case "userFollowingTicket": 
      return getIsUserFollowingTicket() ? "anchor-active" : "anchor-inactive"; 
     default: 
      return null; 
    } 
} 

}

Answer 1

从完整的代码，它看起来像最好的办法是该项目为空，检查完成课后，我们看到它的不注射，和其值仅在onActivate函数中设置，如果contextValue不为null并且projectDao.getByID(contextValue)返回非空值。

能否请您确认在调用之前正确happenning到onActionFromFollowProject