使用 DAO 休眠

Question

我正在使用 Jersey 实现一个 Restful Web 服务。我有一个使用休眠将数据映射到数据库的包。 我是使用 DAO 休眠的新手：

我在 GenericDao 类中有一个方法：

public abstract class GenericDAO<T> extends DAOFactory {

    private final Class classe;

        public GenericDAO(Class classe) {
            this.classe = classe;
        }

           public List<T> findByCriteria(List<Criterion> list) throws Exception {
                Criteria criteria = getSession().createCriteria(classe);
                for (int i = 0; i < list.size(); i++) 
                   criteria.add(list.get(i));
                return criteria.list();
            }
        }

然后我有我的 DAO 类，例如：

public class TaskDAO extends GenericDAO<Task> {

    public TaskDAO() {
        super(Task.class);
    }
}

然后我在 Service 类中使用这个方法，它完全可以像这样工作：

 public Response get(long projectId, String username) {
    List<Criterion> list = new ArrayList<Criterion>();
    Criterion c = Restrictions.eq("project.id", projectId);
    list.add(c);
    List<Deliverable> deliverables = deliverableDAO.findByCriteria(list);
    return deliverables
}

问题出在另一个服务类中的这个方法中：

public Response get(String username) {
    List<Criterion> list = new ArrayList<Criterion>();
    Criterion c = Restrictions.eq("user.username", username);
    list.add(c);
    List<Task> tasks = taskDAO.findByCriteria(list);
    return tasks;
}

如您所见，“Restrictions.eq("project.id", projectId)" 对我来说效果很好，但“Restrictions.eq("user.username", username)" 可能与 'user.username' 有问题，
有什么帮助吗？

堆栈跟踪中的错误是这样的：

javax.ws.rs.WebApplicationException: org.hibernate.QueryException: could not resolve property: user.username of: se.softwerk.timelog.model.Task
    at se.softwerk.controller.services.TaskService.get(TaskService.java:29)
    at se.softwerk.timelog.controller.TaskManager.taskList(TaskManager.java:72)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
    at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:205)
    at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
    at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:288)
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1469)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1400)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339)
    at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:708)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:928)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:539)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:298)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: org.hibernate.QueryException: could not resolve property: user.username of: se.softwerk.timelog.model.Task
    at org.hibernate.persister.entity.AbstractPropertyMapping.propertyException(AbstractPropertyMapping.java:83)
    at org.hibernate.persister.entity.AbstractPropertyMapping.toColumns(AbstractPropertyMapping.java:98)
    at org.hibernate.persister.entity.BasicEntityPropertyMapping.toColumns(BasicEntityPropertyMapping.java:61)
    at org.hibernate.persister.entity.AbstractEntityPersister.toColumns(AbstractEntityPersister.java:1801)
    at org.hibernate.loader.criteria.CriteriaQueryTranslator.getColumns(CriteriaQueryTranslator.java:522)
    at org.hibernate.loader.criteria.CriteriaQueryTranslator.findColumns(CriteriaQueryTranslator.java:537)
    at org.hibernate.criterion.SimpleExpression.toSqlString(SimpleExpression.java:66)
    at org.hibernate.loader.criteria.CriteriaQueryTranslator.getWhereCondition(CriteriaQueryTranslator.java:419)
    at org.hibernate.loader.criteria.CriteriaJoinWalker.<init>(CriteriaJoinWalker.java:123)
    at org.hibernate.loader.criteria.CriteriaJoinWalker.<init>(CriteriaJoinWalker.java:92)
    at org.hibernate.loader.criteria.CriteriaLoader.<init>(CriteriaLoader.java:93)
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1464)
    at org.hibernate.internal.CriteriaImpl.list(CriteriaImpl.java:374)
    at se.softwerk.timelog.model.dao.GenericDAO.findByCriteria(GenericDAO.java:33)
    at se.softwerk.controller.services.TaskService.get(TaskService.java:24)

Answer 1

您需要创建一个连接才能访问任务用户的字段：

criteria.createAlias("user", "theUser");
criteria.add(Restrictions.eq("theUser.username", username);

任务的项目ID不需要做，因为项目ID作为外键直接存储在任务表中。

设计说明：您的 DAO 不会增加太多价值。特别是，它不会将服务类与持久性 API（在本例中为 Hibernate）隔离开来。您可以直接在您的服务类中使用 Hibernate 会话，它不会有太大变化。将服务类与持久性 API 完全隔离是有用的，主要有两个原因：

• 职责更清晰：服务类包含业务逻辑，DAO 包含持久化逻辑
• 它允许模拟 DAO 以便对服务进行单元测试。

Answer 2

您正在使用变量“classe”。它是什么？请显示定义。

您应该为特定类创建 Criteria 实例。所以如果你想返回一个用户对象的列表，你应该重构代码看起来像这样：

public List<T> findByCriteria(Class<?> askFor, List<Criterion> list) throws Exception {
        Criteria criteria = getSession().createCriteria(askFor);
        for (int i = 0; i < list.size(); i++) 
           criteria.add(list.get(i));
        return criteria.list();
    }

然后像这样使用它：

public Response get(String username) {
   List<Criterion> list = new ArrayList<Criterion>();
   Criterion c = Restrictions.eq("user.username", username);
   list.add(c);
   //this will create an alias
   List<Task> tasks = taskDAO.findByCriteria(Task.class, list);
   return tasks;
}

您应该重新设计您的代码，因为您想要实现的是为 Task.user.username 创建一个别名条件。请阅读手册对应部分（15.4）http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/querycriteria.html