运行 HQL 时的类强制转换异常

Question

我有我的Pojo类：

@Entity
@Table(name="INSTITUTE")
public class Institute {    
    private int id;
    private Member member_id;
    private String yearoffrom;
    private Date created_date;
    private Country country_id;
    private State state_id;
    private City city_id;
    private String josh_rating;
    private String institute_type;
    private Clob about; 
    private String tags;
    private String natureofbus;
    private String placement;
    private String placement_percentage;
    private String affiliations;
    private String scholarship;
    private String keyword;
    private String avg_salary;
    private String document_path;
    private String contact_person;
    private String address;
    private String source;
    private String zip;
    private int is_active;
    private int is_deleted;
    private AdminUser created_by_id;
    private AdminUser verified_by_id;

我通过 HQL 只选择几列

select inst.id,inst.member_id.name as institutename,inst.institute_type,inst.city_id.name as cityname,inst.state_id.name as statename,inst.country_id.name as countryname,inst.created_by_id.username as createdby,inst.verified_by_id.username as verifiedby  from Institute inst

在运行代码时，我发现休眠查询是由应用程序生成的，并且正在返回结果集。但是当我想通过以下代码遍历列表时：

for(Institute bean : institutelist) {

应用程序抛出 ClassCastException。

如何解决这个问题？

以下是跟踪跟踪：

SEVERE: Servlet.service() for servlet [spring] in context with path [/EducationNew] threw exception [Request processing failed; nested exception is java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to education.bean.Institute] with root cause
java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to education.bean.Institute
    at education.service.InstituteListingService.getInstituteList_HQL(InstituteListingService.java:45)
    at education.controller.LoginController.validateUser(LoginController.java:54)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:436)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:424)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    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:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
    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:1004)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)

HQL 查询：休眠：select * from ( select institute0_.id as col_0_0_, member1_.name as col_1_0_, institute0_.institute_type as col_2_0_, city2_.name as col_3_0_, state3_.name as col_4_0_, country4_.name as col_5_0_, adminuser5_.username as col_6_0_, adminuser6_.username as col_7_0_ from INSTITUTE institute0_, MEMBER member1_, City city2_, State state3_, Country country4_, AdminUser adminuser5_, AdminUser adminuser6_ where institute0_.member_id=member1_.id and institute0_.city_id=city2_.id and institute0_.state_id=state3_.id and institute0_.country_id=country4_.id and institute0_.created_by_id=adminuser5_.id and institute0_.verified_by_id=adminuser6_.id ) where rownum <= ?

Answer 1

您的查询当前会返回一个对象的结果列表，这些对象不是研究所的实例 - 由于别名，如 inst.member_id.name 作为机构名称，选择成员名称而不是成员本身等。

如何解决？解决方案很少，但我会尝试选择研究所进入新研究所：

Query query = session.createQuery("Select new Institute(inst.id, inst.name, inst.stuff...) from Institute inst");

完整的示例可以在这里找到

另一种解决方案是使用Hibernate投影。

Answer 2

如果你有选择地选择某些属性而不是选择整个实体，则返回的实际上是元组列表（List<Object[]>）。 列表中的每个条目（即Object[]）代表一行结果。

因此，您的循环应如下所示

List<Object[]> results = (List<Object[]>) yourQuery.list();
for (Object[] result : results) {
    //....
}

引自 http://docs.jboss.org/hibernate/orm/4.3/manual/en-US/html/ch16.html#queryhql-select：

查询可以返回多个对象和/或属性作为数组 类型对象[]：

select mother, offspr, mate.name from DomesticCat as mother
inner join mother.mate as mate
left outer join mother.kittens as offspr

引用的链接中还描述了处理选择选择性属性的更多方法