如何让HIbernate获取根实体的所有属性以及只有关联实体的特定属性？

本文介绍了如何让HIbernate获取根实体的所有属性以及只有关联实体的特定属性？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我有根实体 strong> 我尝试使用 $ b 使用 criteria.list（）获得的列表是 List<< ; Object []> 其行是 [Hostel，Integer，String，String] 您可以使用 Criteria 获得某些内容，但是 Criteria 比查询更严格。我找不到任何允许混合实体和字段的API。所以据我所知，不可能获得包含实体（Hostels）的行和来自关联（owner.userId，owner.firstName，owner.lastName）的单独字段。 我能想象的唯一方法是明确列出Hostels的所有字段： criteria.createAlias（所有者，所有者，JoinType.LEFT_OUTER_JOIN） .setProjection（ Projections.projectionList（） .add（Projections.property（hostelId）） .add（ Projections.property（country）） .add（Projections.property（endDate）） ... ... Hostel的所有其他属性 .. 。 .add（Projections.property（owner.userId）） .add（Projections.property（owner.firstName）） .add（Projections.property（owner 。姓）））; 您可以使用元数据将它自动化一点（不要忘记ID ...）注意：如果直接使用标量值，我可以使用别名投影方式稍后才能使用包装类，您可以放心地省略 Projection.alias ： ProjectionList hostelProj = Projections.projectionList（）; String id = sessionFactory.getClassMetadata（Hostel.class） .getIdentifierPropertyName（）; hostelProperties.add（Projections.alias（Projections.property（id），id））; for（String prop：sessionFactory.getClassMetadata（Hostel.class）.getPropertyNames（））{ hostelProperties.add（Projections.alias（Projections.property（prop），prop））; } Criteria criteria = session.createCriteria（Hostel.class）; criteria.createAlias（owner，owner，JoinType.LEFT_OUTER_JOIN）; criteria.setProjection（ Projections.projectionList（） .add（hostelProj） .add（Projections.property（owner.id）） .add （Projections.property（owner.firstName）） .add（Projections.property（owner.lastName）））; List list = criteria.list（）; 这种方式可以正确生成 但是您将无法使用条件。 setResultTransformer（Criteria.ALIAS_TO_ENTITY_MAP），因为结果集不完全是来自 Hostel （即使没有别名）的字段的图像。 事实上，列表是一个 List< Object []> ，其中包含 Hostel 后面跟着所有者中的3个必填字段。 您将不得不添加一个包含 Hostel 以及其他三个字段可以使用 AliasToBeanResultTransformer 并且获得真实 Hostel public class HostelWrapper { private hostel hostel; private int owner_id; 私人字符串owner_firstName; 私人字符串owner_lastName; public HostelWrapper（）{ hostel = new Hostel（）; } public Hostel getHostel（）{ return hostel; } public void setId（int id）{ hostel.setId（id）; } public void setOwner（User owner）{ hostel.setOwner（owner）; } //其他设置者为Hostel字段... public int getOwner_id（）{ return owner_id; } public void setOwner_id（Integer owner_id）{ //注意：由于外连接可能为空 this.owner_id =（owner_id == null）？ 0：owner_id; } //名字和姓氏的获得者和设置者... } 然后你可以写成： criteria.setResultTransformer（new AliasToBeanResultTransformer（HostelWrapper.class））; 列表< HostelWrapper> hostels = criteria.list（）; 宿舍= hostels.get（0）.getHostel（）; 字符串firstName = hostels.get（0）.getFirstName（）; 我可以验证没有所有者 hostel.getOwner（）为空，当有一个时， hostel.getOwner（）。getId（）等于 getOwner_id（） / code>，并且此访问不会生成任何额外的查询。但是任何对 hostel.getOwner（），甚至 firstName 或 lastName字段的访问会生成一个，因为用户实体未在会话中加载。 用法应该是： pre $ for（HostelWrapper hostelw：criteria.list（））{ Hostel hostel = hostelw.getHostel （）; //使用hostel，hostelw.getOwner_firstName和hostelw.getOwner_lastName } I have root entity Hostel and its single association User owner.When I fetch Hostel entity I need to eagerly fetch User owner, but only owner's 3 properties : userId,firstName,lastName.For now my criteria query is :Criteria criteria = currenSession().createCriteria(Hostel.class);criteria.add(Restrictions.ge("endDate", Calendar.getInstance()));if (StringUtils.notNullAndEmpty(country)) { criteria.add(Restrictions.eq("country", country));}Long count = (Long) criteria .setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY) .setProjection(Projections.rowCount()).uniqueResult();criteria.setFetchMode("owner", FetchMode.SELECT);criteria.addOrder(Order.desc("rating"));// needed to reset previous rowCount projectioncriteria.setProjection(null);// retrieve owner associationcriteria.createAlias("owner", "owner", JoinType.LEFT_OUTER_JOIN) .setProjection( Projections.projectionList() .add(Projections.property("owner.userId")) .add(Projections.property("owner.firstName")) .add(Projections.property("owner.lastName")));criteria.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP);Next, I do criteria.list() and I get sql statement which selects only owner's 3 properties as specified in projection list. But it doesn't select any property of root Hostel entity.Generated query is:select owner1_.user_id as y0_, owner1_.firstName as y1_, owner1_.lastName as y2_ from HOSTEL this_ left outer join USER owner1_ on this_.owner_fk=owner1_.user_id where this_.end_date>=? and this_.country=? order by this_.rating desc limit ?This query doesn't work because it returns five Maps which are empty. FIve maps are because there are five Hostel rows that match where condition. I created simple sql query and it works fine so the problem is only here.How to force hibernate to fetch all properties of root Hostel entity and only 3 properties of asociated User owner entity?EDITI tried to use getSessionFactory().getClassMetadata(Hostel.class) but it gave error about mapping enum in Hostel. So I fallback to list Hostel properties manually. For now my criteria query is:// retrieve owner association criteria.createAlias("owner", "owner", JoinType.LEFT_OUTER_JOIN); criteria.setProjection(Projections.projectionList() .add(Projections.property("hostelId")) .add(Projections.property("address")) .add(Projections.property("country")) .add(Projections.property("region")) .add(Projections.property("gender")) .add(Projections.property("owner.userId")) .add(Projections.property("owner.firstName")) .add(Projections.property("owner.lastName")));List<Hostel> hostels = criteria.list();for (Hostel hostel : hostels) { // at this line I get error java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.home.hostme.entity.Hostel User owner = hostel.getOwner(); System.out.println("owner=" + owner); }Note that I removed ALIAS_TO_ENTITY_MAP result transformer. This generated such mysql query :select this_.hostel_id as y0_, this_.address as y1_, this_.country as y2_, this_.region as y3_, this_.gender as y4_, owner1_.user_id as y5_, owner1_.firstName as y6_, owner1_.lastName as y7_ from HOSTEL this_ left outer join USER owner1_ on this_.owner_fk=owner1_.user_id where this_.end_date>=? and this_.country=? order by this_.rating desc limit ?At for-each loop get such an error:java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.home.hostme.entity.Hostel at com.home.hostme.dao.impl.HostelDaoImpl.findHostelBy(HostelDaoImpl.java:168) 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 org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317) at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150) at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:155) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204) at com.sun.proxy.$Proxy64.findHostelBy(Unknown Source) at com.home.hostme.service.HostelService.findHostelBy(HostelService.java:27) at com.home.hostme.service.HostelService$$FastClassByCGLIB$$74db5b21.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:698) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150) at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:96) at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:260) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:94) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:631) at com.home.hostme.service.HostelService$$EnhancerByCGLIB$$7af3bc10.findHostelBy(<generated>) at com.home.hostme.web.hostel.HostelController.doSearch(HostelController.java:94) 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 org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936) at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:838) at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812) 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.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) 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:502) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)This error means that I don't have type Hostel in resulting list hostels.I even tried to find out class of elements in resulting list 'hostels' with this:List hostels = criteria.list(); System.out.println("firstRow.class=" + hostels.get(0).getClass());It printed:firstRow.class=class [Ljava.lang.Object;Then I tried to set ALIAS_TO_ENTITY_MAP for new ProjectionList, but resulting list 'hostels' was:[{}, {}, {}, {}, {}]Five empty maps. Five because there are 5 rows in db(table hostel) matching where clause.Then I deleted projection list completely and hibernate retrieved 5 hostels and 5 associated User owners and owner's images as expected. THE PROBLEM is how to stop hibernate retrieve associated Image entity of associated User owner. The best would be to fetch only 3 specific props of associated User owner. Thank you! 解决方案 You can do it with a direct query :Query query = session.createQuery("SELECT hostel, owner.id, owner.firstname, " +"owner.lastname FROM Hostel hostel LEFT OUTER JOIN hostel.ower AS owner");List list = query.list();generates a SQL like :with all the fields from Hostel and only required fields from User.The list obtained with criteria.list() is a List<Object[]> whose rows are [ Hostel, Integer, String, String]You can obtain something using Criteria, but Criteria are more strict than queries. I could not find any API that allows to mix entities and fields. So as far as I know, it is not possible to get rows containing an entity (Hostels) and separate fields from an association (owner.userId, owner.firstName, owner.lastName).The only way I can imagine would be to explicitely list all fields from Hostels :criteria.createAlias("owner", "owner", JoinType.LEFT_OUTER_JOIN) .setProjection( Projections.projectionList() .add(Projections.property("hostelId")) .add(Projections.property("country")) .add(Projections.property("endDate")) ... ... all other properties from Hostel ... .add(Projections.property("owner.userId")) .add(Projections.property("owner.firstName")) .add(Projections.property("owner.lastName")));You can automate it a little by using Metadata (don't forget the id ...) - note : I use aliased projection only to be able later to use a wrapper class, if you directly use the scalar values, you can safely omit the Projection.alias : ProjectionList hostelProj = Projections.projectionList(); String id = sessionFactory.getClassMetadata(Hostel.class) .getIdentifierPropertyName(); hostelProperties.add(Projections.alias(Projections.property(id),id)); for (String prop: sessionFactory.getClassMetadata(Hostel.class).getPropertyNames()) { hostelProperties.add(Projections.alias(Projections.property(prop), prop)); } Criteria criteria = session.createCriteria(Hostel.class); criteria.createAlias("owner", "owner", JoinType.LEFT_OUTER_JOIN); criteria.setProjection( Projections.projectionList() .add(hostelProj) .add(Projections.property("owner.id")) .add(Projections.property("owner.firstName")) .add(Projections.property("owner.lastName"))); List list = criteria.list();That way correctly generates But you will not be able to use criteria.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP) because the resultset is not exactly the image of the fields from Hostel (even without the aliases).In fact the list is a List<Object[]> with rows containing all individual fields from Hostel followed by the 3 required fields from owner.You will have to add a wrapper class containing a Hostel and the 3 other fields to make use of an AliasToBeanResultTransformer and get true Hostel objects :public class HostelWrapper { private Hostel hostel; private int owner_id; private String owner_firstName; private String owner_lastName; public HostelWrapper() { hostel = new Hostel(); } public Hostel getHostel() { return hostel; } public void setId(int id) { hostel.setId(id); } public void setOwner(User owner) { hostel.setOwner(owner); } // other setters for Hostel fields ... public int getOwner_id() { return owner_id; } public void setOwner_id(Integer owner_id) { // beware : may be null because of outer join this.owner_id = (owner_id == null) ? 0 : owner_id; } //getters and setters for firstName and lastName ...}And then you can successfully write :criteria.setResultTransformer(new AliasToBeanResultTransformer(HostelWrapper.class));List<HostelWrapper> hostels = criteria.list();Hostel hostel = hostels.get(0).getHostel();String firstName = hostels.get(0).getFirstName();I could verify that when there is no owner hostel.getOwner() is null, and when there is one, hostel.getOwner().getId() is equal to getOwner_id() and that this access does not generate any extra query. But any access to an other field of hostel.getOwner(), even firstName or lastName generates one because the User entity was not loaded in session.The most common usage should be : for (HostelWrapper hostelw: criteria.list()) { Hostel hostel = hostelw.getHostel(); // use hostel, hostelw.getOwner_firstName and hostelw.getOwner_lastName} 这篇关于如何让HIbernate获取根实体的所有属性以及只有关联实体的特定属性？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！