Java Play Framework应用程序不断在第6行抛出空指针

我试图在Play框架中创建一个简单的论坛系统，但我以一种奇怪的方式得到了一个错误。我有一个forum.java类，它是错误的来源，但是不管里面的代码是什么，它总是在第6行抛出一个空指针。我认为，这里有尽可能多的相关信息

package models;

import io.ebean.Finder;
import io.ebean.Model;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import java.util.List;

@Entity
public class Forum extends Model {

    @Id
    private String id;

    @ManyToOne(cascade = CascadeType.ALL)
    private List<Thread> threads;

Stacktrace v2：

[error] application -

! @77hpce3hh - Internal server error, for (GET) [/forum/1] ->

play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[PersistenceException: Query threw SQLException:Column "T1.FORUM_ID" not found; SQL statement:
select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id  where t0.id = ?   order by t0.id [42122-196] Bind values:[null] Query was:select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id  where t0.id = ?   order by t0.id]]
        at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:255)
        at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:182)
        at play.core.server.AkkaHttpServer$$anonfun$2.applyOrElse(AkkaHttpServer.scala:320)
        at play.core.server.AkkaHttpServer$$anonfun$2.applyOrElse(AkkaHttpServer.scala:318)
        at scala.concurrent.Future.$anonfun$recoverWith$1(Future.scala:414)
        at scala.concurrent.impl.Promise.$anonfun$transformWith$1(Promise.scala:37)
        at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
        at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55)
        at akka.dispatch.BatchingExecutor$BlockableBatch.$anonfun$run$1(BatchingExecutor.scala:91)
        at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
Caused by: javax.persistence.PersistenceException: Query threw SQLException:Column "T1.FORUM_ID" not found; SQL statement:
select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id  where t0.id = ?   order by t0.id [42122-196] Bind values:[null] Query was:select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id  where t0.id = ?   order by t0.id
        at io.ebean.config.dbplatform.SqlCodeTranslator.translate(SqlCodeTranslator.java:48)
        at io.ebean.config.dbplatform.DatabasePlatform.translate(DatabasePlatform.java:195)
        at io.ebeaninternal.server.query.CQueryEngine.translate(CQueryEngine.java:139)
        at io.ebeaninternal.server.query.DefaultOrmQueryEngine.translate(DefaultOrmQueryEngine.java:38)
        at io.ebeaninternal.server.core.OrmQueryRequest.translate(OrmQueryRequest.java:81)
        at io.ebeaninternal.server.query.CQuery.createPersistenceException(CQuery.java:666)
        at io.ebeaninternal.server.query.CQueryEngine.find(CQueryEngine.java:422)
        at io.ebeaninternal.server.query.DefaultOrmQueryEngine.findId(DefaultOrmQueryEngine.java:162)
        at io.ebeaninternal.server.core.OrmQueryRequest.findId(OrmQueryRequest.java:327)
        at io.ebeaninternal.server.core.DefaultServer.findId(DefaultServer.java:1175)
Caused by: org.h2.jdbc.JdbcSQLException: Column "T1.FORUM_ID" not found; SQL statement:
select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id  where t0.id = ?   order by t0.id [42122-196]
        at org.h2.message.DbException.getJdbcSQLException(DbException.java:345)
        at org.h2.message.DbException.get(DbException.java:179)
        at org.h2.message.DbException.get(DbException.java:155)
        at org.h2.expression.ExpressionColumn.optimize(ExpressionColumn.java:147)
        at org.h2.command.dml.Select.prepare(Select.java:839)
        at org.h2.command.Parser.prepareCommand(Parser.java:263)
        at org.h2.engine.Session.prepareLocal(Session.java:578)
        at org.h2.engine.Session.prepareCommand(Session.java:519)
        at org.h2.jdbc.JdbcConnection.prepareCommand(JdbcConnection.java:1204)
        at org.h2.jdbc.JdbcPreparedStatement.<init>(JdbcPreparedStatement.java:73)

线路

at io.ebeaninternal.server.deploy.BeanPropertyAssocMany.createReference(BeanPropertyAssocMany.java:652)

可以帮助您了解此处的错误：

您误用了@ManyToOne注释

在您的应用程序中，一个论坛可以容纳多个线程，因此论坛模型中线程列表上方的注释应该是

@OneToMany

您还需要将线程模型中论坛声明上方的注释切换为

---

请注意，在这里搜索NullPointerException的人：如果忘记将@DbArray标记添加到字段中，同样的问题也会发生。

运行clean命令，您的类可能不是最新的。不幸的是，我已经尝试过了。通常这是我去修复像这样奇怪的东西，但它似乎不起作用。我会让小组中的其他人试着运行它，看看我的环境是否有问题。你能在你的问题中包含完整的堆栈跟踪吗？是的。把它添加到问题中。在上下文中，这种情况发生的时间是我加载论坛页面时。我有一系列的子论坛，每当我点击进入其中一个子论坛时，它都会确定要在论坛视图中加载哪个论坛，然后获取发布在那里的线程列表。在io.ebeanternal.server.deploy.beanproperty assocmany上，我认为您定义了一个多通、一通或多通错误。你可能想检查一下。这是一个评论，不是一个答案。@Gerardo谁真的在乎呢

@OneToMany

@ManyToOne