Hibernate的預測不同的記錄

我需要在我現有的項目訪問唯一的記錄，但問題是，當我使用Hibernate的預測不同的記錄

cr = session.createCriteria(Application.class); 
    cr.add(Restrictions.eq("verified", "Yes")); 
cr.setProjection(Projections.distinct(Projections.property("application_name")));

它給我錯誤

java.lang.String cannot be cast to org.entitybean.Application

這裏是我的迭代器

List<Application> result = cr.list(); 
for (Iterator it = result.iterator(); it.hasNext();) { 
       Application ap = (Application) it.next(); 
      List<ApplicationPricing> app = (List<ApplicationPricing>) ap 
        .getApplicationpricing(); 
      List<ApplicationDownloads> app_downloads = (List<ApplicationDownloads>) ap 
        .getApplicationdownloads(); 
      List<ApplicationComments> app_comments = (List<ApplicationComments>) ap 
        .getApplicationcomments(); 
      List<ApplicationRating> app_rating = (List<ApplicationRating>) ap 
        .getApplicationrating(); 

      ApplicationBean ab = new ApplicationBean(); 
      ab.setNo_of_records(count + ""); 
      ab.setApp_id(ap.getApp_id() + ""); 

... 
}

這是完整的堆棧跟蹤：

java.lang.ClassCastException: java.lang.String cannot be cast to org.block.entitybean.Application 
    at org.block.businesslogic.ApplicationLogic.getApplicationDetails(ApplicationLogic.java:933) 
    at org.block.actions.ApplicationAction.appsDetGet(ApplicationAction.java:155) 
    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.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:452) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:291) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:254) 
    at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263) 
    at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:133) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:142) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:166) 
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187) 
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52) 
    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:485) 
    at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77) 
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91) 
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) 
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) 
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) 
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) 
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) 
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606) 
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) 
    at java.lang.Thread.run(Unknown Source)

來源

2013-11-09 Sdf Sdf

首先，發表您的整個堆棧跟蹤。其次，只要你使用一個普通的'List '，使用'Iterator '（或增強的for'循環）;沒有必要讓你自己施放。 – chrylis

該條件已經返回條目的專用實例，因此不需要額外的轉換。 Foreach語句應該應用於迭代器提取值的位置。 –

問題（例外）由以下事實引起的，所使用的預測，其導致一個匿名對象陣列中，當List()稱爲英寸我們在這種情況下需要的是ResultTransformer。有關詳細信息，讓我們在這裏看看5.2.3. ResultTransformer

一些摘錄：

...特別是在使用投影時，由查詢（在這種情況下一個對象數組）返回的數據結構，是不是始終匹配應用程序需求。它可以應用使用ResultTransformer 手術後的查詢相匹配的目標數據結構...

所以，在我們的例子，之前我們所說的列表中，我們應該

... 
cr 
.setResultTransformer(Transformers.aliasToBean(Application.class)) 
.list();

我們也有調整，是提供別名投影，該屬性的名稱，它是代表

... 
cr.setProjection(Projections.distinct(Projections.property("application_name")) 
    , ""application_name");

但這最有可能的不會解決真正的問題。我的意思是，我們需要獲得幾乎完全填充的應用程序的列表（定價，下載）。因爲在這個時候，List<Application>將包含非常有限的信息量。實際上，只有application_name屬性會被填充。

我會建議的是改變方法。嘗試創建某種子查詢。例如選擇不同的（最大，最小）application_Id，按application_name分組。然後用它來獲得應用程序，其中Id是IN子查詢。其出發點如何可以做到：

17.10. Detached queries and subqueries ...文檔
How to use a subquery ... the accepted answer作爲一個例子

來源

2013-11-09 17:41:33

Hibernate的預測不同的記錄

回答

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