Question

我是Play的新手，我正在努力实现Canteen和OpeningTimes之间的OneToOne关系，我想1：1就是我想要的。但是我得到一个NullPointerException ...

@Entity
public class OpeningTimes extends Model {

   @Id
   public Long id;

   @Required
   public String mondayHours;

   @Required
   public String tuesdayHours;

       ...

   @OneToOne
   public Canteen canteen;

}

@Entity
public class Canteen extends Model {

   @Id
   public Long id;

   ...  

   @OneToOne
   public OpeningTimes openingTimes;

}

这里我填充了数据库

public class Global extends GlobalSettings {

@Override
public void onStart(Application arg0) {
    if(Canteen.finder.findRowCount() == 0) {

        Canteen canteen = new Canteen();
        ...
        canteen.save();


        Canteen canteen1 = new Canteen();
        ...
        canteen1.save();


        OpeningTimes times = new OpeningTimes();
        times.mondayHours = "7:00 - 15:00";
        times.tuesdayHours = "7:00 - 15:00";
        ...
        times.canteen = canteen;
        times.save();


        OpeningTimes times1 = new OpeningTimes();
        times1.mondayHours = "7:00 - 15:00";
        times1.tuesdayHours = "7:00 - 15:00";
        ...
        times1.canteen = canteen1;
        times1.save();

}

show.scala.html

@(canteen: Canteen)

@main("MamHlad | " + canteen.nameShort) {

   <h1>@canteen.nameFull</h1>

   <h2>Opening times</h2>
   ** <p>@canteen.openingTimes.mondayHours</p> **
   <p>@canteen.openingTimes.tuesdayHours</p>
}

Asterixes标记它抛出NullPointerException的行，这里是堆栈跟踪

! @6c6cgmg4b - Internal server error, for request [GET /canteens/2] ->

play.core.ActionInvoker$$anonfun$receive$1$$anon$1: Execution exception [[NullPointerException: null]]
        at play.core.ActionInvoker$$anonfun$receive$1.apply(Invoker.scala:134) [play_2.9.1.jar:2.0.4]
        at play.core.ActionInvoker$$anonfun$receive$1.apply(Invoker.scala:115) [play_2.9.1.jar:2.0.4]
        at akka.actor.Actor$class.apply(Actor.scala:318) [akka-actor.jar:2.0.2]
        at play.core.ActionInvoker.apply(Invoker.scala:113) [play_2.9.1.jar:2.0.4]
        at akka.actor.ActorCell.invoke(ActorCell.scala:626) [akka-actor.jar:2.0.2]
        at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:197) [akka-actor.jar:2.0.2]
Caused by: java.lang.NullPointerException: null
        at views.html.show$.apply(show.template.scala:37) ~[classes/:na]
        at views.html.show$.render(show.template.scala:105) ~[classes/:na]
        at views.html.show.render(show.template.scala) ~[classes/:na]
        at controllers.Application.show(Application.java:23) ~[classes/:na]
        at Routes$$anonfun$routes$1$$anonfun$apply$5$$anonfun$apply$6.apply(routes_routing.scala:76) ~[classes/:na]
        at Routes$$anonfun$routes$1$$anonfun$apply$5$$anonfun$apply$6.apply(routes_routing.scala:76) ~[classes/:na]

提前感谢您的帮助！

Answer 1

我发现你没有指定OneToOne关系的拥有方，这是强制性的。

@Entity
public class OpeningTimes extends Model {

   @Id
   public Long id;
      ...

   @OneToOne(mappedBy="openingTimes", cascade=CascadeType.ALL)
   public Canteen canteen;
}

另外我认为你需要使用setOpeningTimes方法，而不是直接访问属性。像这样，

canteen.setOpeningTimes(openingTime1);
canteen.save();

这是一个例子： https://ebeanorm.svn.sourceforge.net/svnroot/ebeanorm/ebean/trunk/src/test/java/com/avaje/tests/basic/TestMultipleOneToOneIUD.java

玩！ 2.0 - OneToOne关系 - NullPointerException

1 个答案: