Question

我在使用hibernate的资源类中有很多关系。在Category类中：

@Entity
public class Category {

    Id
    @GeneratedValue
    private long id;

    @ManyToMany
    @JoinTable(name = "category_activity", 
    joinColumns = { @JoinColumn(name = "Category_id") }, 
    inverseJoinColumns = { @JoinColumn(name = "activities_id") })
    private Collection<Activity> activities;
}

在Activity类中：

@Entity
public class Activity {

    @Id
    @GeneratedValue
    private long id;

    @ManyToMany
    @JoinTable(name="category_activity", 
    joinColumns={@JoinColumn(name="activities_id")},
    inverseJoinColumns={@JoinColumn(name="Category_id")})
    private Collection<Category> category;
}

当我在他们之间有一个ToMany关系时，我使用了一个对我来说很好的查询：

Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
Collection<Activity> activities = (Collection<Activity>) session.createQuery("from Activity as a where a.category.id=" + categoryId + " order by a.key").list();
session.getTransaction().commit();

我感谢您为ManyToMany关系修复此查询的任何帮助吗？

我也使用了这个查询：

activities = (List<Activity>) session.createQuery("from Activity a join a.category cs where cs.id= :categoryId order by a.key").setLong("categoryId", categoryId).list();

我在堆栈跟踪中遇到了这个错误：

<html><head><title>Apache Tomcat/7.0.23 - Error report</title><style><!--H1 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:22px;} H2 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:16px;} H3 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:14px;} BODY {font-family:Tahoma,Arial,sans-serif;color:black;background-color:white;} B {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;} P {font-family:Tahoma,Arial,sans-serif;background:white;color:black;font-size:12px;}A {color : black;}A.name {color : black;}HR {color : #525D76;}--></style> </head><body><h1>HTTP Status 500 - </h1><HR size="1" noshade="noshade"><p><b>type</b> Exception report</p><p><b>message</b> <u></u></p><p><b>description</b> <u>The server encountered an internal error () that prevented it from fulfilling this request.</u></p><p><b>exception</b> <pre>java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to java.lang.Comparable
    java.util.ComparableTimSort.countRunAndMakeAscending(Unknown Source)
    java.util.ComparableTimSort.sort(Unknown Source)
    java.util.ComparableTimSort.sort(Unknown Source)
    java.util.Arrays.sort(Unknown Source)
    java.util.Collections.sort(Unknown Source)
    se.softwerk.timelog.controller.ActivityManager.activityList2(ActivityManager.java:64)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
    com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:205)
    com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
    com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:288)
    com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
    com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
    com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1469)
    com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1400)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339)
    com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:708)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
</pre></p><p><b>note</b> <u>The full stack trace of the root cause is available in the Apache Tomcat/7.0.23 logs.</u></p><HR size="1" noshade="noshade"><h3>Apache Tomcat/7.0.23</h3></body></html>

Answer 1

首先，你不应该连接字符串，这为SQLInjection attacks打开了大门，你应该使用命名参数。更多关于named parameters here

其次，如果你有ManyToMany关系，那么双方应该是多元化的：

此

private Collection<Category> category;

应该是这样的：

private Collection<Category> categories;

现在就你的具体问题，你有这个

from Activity as a where a.category.id= :categoryId order by a.key

你需要这个：

from Activity a join a.category cs where cs.id= :categoryId  order by a.key

使用hibernate查询多对多关系

1 个答案: