我有根实体旅馆
及其单个关联用户所有者
。
当我获取Hotel
实体时,我需要急切地获取用户所有者
,但只有所有者
的3个属性:userId、afstName、lastName。
现在我的标准查询是:
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 projection
criteria.setProjection(null);
// retrieve owner association
criteria.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);
接下来,我执行标准。list()
,我得到了sql语句,它只选择了投影列表中指定的owner
的3个属性。但它不选择根<code>Hostel</code>实体的任何属性。生成的查询为:
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 ?
此查询不起作用,因为它返回五个空的Map
。五个映射是因为有五个<code>Hostel</code>行符合where条件。我创建了一个简单的sql查询,它工作得很好,所以问题只在这里。
如何强制Hibernate以获取rootHotel
实体的所有属性,而只有3个属性的已分类用户所有者
实体?
编辑我尝试使用getSessionFactory().getClassMetadata(Hostel.class),
但它给出了有关在Hostel
中映射枚举的错误。所以我回退到手动列出旅馆
属性。目前,我的条件查询是:
// 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);
}
请注意,我移除了< code>ALIAS_TO_ENTITY_MAP结果转换器。这生成了这样的mysql查询:
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 ?
在for-each循环中得到这样一个错误:
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)
此错误意味着我在结果列表中没有
旅馆类型。
我什至试图找出结果列表“旅馆”中的元素类:
List hostels = criteria.list();
System.out.println("firstRow.class=" + hostels.get(0).getClass());
它打印了:
firstRow.class=class [Ljava.lang.Object;
然后,我尝试设置ALIAS_TO_ENTITY_MAP
为新的项目列表,但结果列表'旅馆'是:
[{}, {}, {}, {}, {}]
五张空地图。五行,因为db(table hostel)中有5行匹配where子句。
然后我完全删除了投影列表,Hibernate按预期检索了5个主机和5个相关的用户所有者
和所有者
的图像。
问题是如何停止Hibernate检索关联用户所有者
的关联图像
实体。最好的办法是只获取关联用户所有者
的 3 个特定道具。
谢谢!
据我观察,你不可能得到你想要的结果。
我们可以使用以下步骤完成:
String[] propertyNames = sessionFactory.getClassMetadata(Hostel.class).getPropertyNames();
ProjectionList projectionList = Projections.projectionList();
for (String propString : propertyNames) {
projectionList.add(Projections.property(propString));
}
请按以下方式更改代码
criteria.createAlias("owner", "owner", JoinType.LEFT_OUTER_JOIN)
.setProjection(
projectionList
.add(Projections.property("owner.userId"))
.add(Projections.property("owner.firstName"))
.add(Projections.property("owner.lastName")));
请试着知道。
@Serge Ballesta解决了我的问题,但这是我的最终工作代码:
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();
// mark query as readonly
criteria.setReadOnly(true);
// descendingly sort result by rating property of Hostel entity
criteria.addOrder(Order.desc("rating"));
// reset rowCount() projection
criteria.setProjection(null);
ProjectionList hostelProjList = Projections.projectionList();
ClassMetadata hostelMetadata = getSessionFactory().getClassMetadata(
Hostel.class);
// add primary key property - hostelId
hostelProjList.add(Projections.property(hostelMetadata
.getIdentifierPropertyName()), "hostelId");
// add all normal properties of Hostel entity to retrieve from db
for (String prop : hostelMetadata.getPropertyNames()) {
//skip associations
if (!prop.equals("owner") && !prop.equals("images")
&& !prop.equals("requests") && !prop.equals("feedbacks"))
hostelProjList.add(Projections.property(prop), prop);
}
// add properties of User owner association to be retrieved
hostelProjList
.add(Projections.property("owner.userId"), "owner_id")
.add(Projections.property("owner.firstName"), "owner_firstName")
.add(Projections.property("owner.lastName"), "owner_lastName");
// create alias to retrieve props of User owner association
criteria.createAlias("owner", "owner", JoinType.LEFT_OUTER_JOIN);
criteria.setProjection(hostelProjList);
criteria.setResultTransformer(new AliasToBeanResultTransformer(
HostelWrapper.class));
List<HostelWrapper> wrappers = criteria.list();
我的< code>HostelWrapper是:
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 setHostelId(Integer hostelId) {
this.hostel.setHostelId(hostelId);
}
public void setCountry(String country) {
this.hostel.setCountry(country);
}
public int getOwner_id() {
return owner_id;
}
public void setOwner_id(Integer owner_id) {
this.owner_id = owner_id == null ? 0 : owner_id;
}
public String getOwner_firstName() {
return owner_firstName;
}
public void setOwner_firstName(String owner_firstName) {
this.owner_firstName = owner_firstName;
}
public String getOwner_lastName() {
return owner_lastName;
}
public void setOwner_lastName(String owner_lastName) {
this.owner_lastName = owner_lastName;
}
< code > aliastobeenresulttransformer 使用此< code>HostelWrapper将hibernate结果集映射到实体。
我最后的结论是,当你想设定联想的投影时,HQL是正确的选择。使用< code > aliastobeenresulttransformer ,您可以绑定到属性名称,使用hql也是一样。好处是HQL更容易写。
您可以通过直接查询来做到这一点:
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();
生成如下SQL语句:
选择hostel0。id为col_0_0_,user1_。id为col_1_0_,user1_。名为col_2_0_,user1_。姓col_3_0,hostel0。id为id1_0_,hostel0_。名称为name2_0_,…,hostel0_。Hostel hostel0_的owner_id作为user_id4_0_左外侧加入user1_上的用户user1_。id=hostel0_.owner_id
包含旅馆的所有字段,只有用户的必填字段。
使用条件获得的列表。list()
是一个列表
您可以使用
Criteria
获得一些信息,但Criteria
比查询更严格。我找不到任何允许混合实体和字段的API。因此,据我所知,不可能获取包含实体(Hostels)的行以及与关联(owner.userId、owner.firstName、owner.lastName)分开的字段。
我可以想象的唯一方法是明确列出Hostels的所有字段:
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")));
您可以通过使用元数据(不要忘记id...)-注意:我使用别名投影只是为了以后能够使用包装类,如果您直接使用标量值,可以安全地省略< code>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();
这样才能正确地生成
选择this_。id为y0_,this_。名称为y1_,…,this_。user_id为y3_,owner_。id为y4_,所有者1_。名为y5_,所有者__。姓y6_来自酒店this_left外部加入用户owner1_在this_.user_id=owner1.id
但是您将无法使用 criteria.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP),
因为结果集并不完全是 Hostel
中字段的图像(即使没有别名)。事实上,列表是一个列表
您必须添加一个包含< code>Hostel
和其他3个字段的包装类,才能使用< code > aliastobeenresulttransformer 并获得真正的< code>Hostel对象:
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 ...
}
然后您可以成功编写:
criteria.setResultTransformer(new AliasToBeanResultTransformer(HostelWrapper.class));
List<HostelWrapper> hostels = criteria.list();
Hostel hostel = hostels.get(0).getHostel();
String firstName = hostels.get(0).getFirstName();
我可以验证当没有所有者时< code>hostel.getOwner()为空,当有所有者时,< code>hostel.getOwner()为空。getId()等于< code>getOwner_id(),并且该访问不会生成任何额外的查询。但是对< code>hostel.getOwner()的其他字段的任何访问,甚至是< code>firstName或< code>lastName都会生成一个,因为< code>User实体没有在会话中加载。
最常见的用法应该是:
for (HostelWrapper hostelw: criteria.list()) {
Hostel hostel = hostelw.getHostel();
// use hostel, hostelw.getOwner_firstName and hostelw.getOwner_lastName
}
问题内容: 我有根实体及其单一关联。 当我获取实体时,我需要热切地获取,但是只有它的3个属性:userId,firstName,lastName。 现在,我的条件查询是: 接下来,我得到了sql语句,该语句仅选择投影列表中指定的3个属性。但是它不会选择根实体的任何属性。生成的查询是: 该查询不起作用,因为它返回了五个为空的。五个映射是因为有五行匹配where条件。我创建了简单的sql查询,它工作正
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