如何使HIbernate获取根实体的所有属性并仅获取关联实体的特定属性？

时间：2014-08-16 07:16:04

标签： java hibernate hibernate-criteria

我有根实体Hostel及其单一关联User owner。

当我提取Hostel实体时，我需要急切地提取User owner，但只有owner的3个属性：userId，firstName，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，我做criteria.list()并获得sql语句，该语句仅选择投影列表中指定的owner 3个属性。但它并没有选择根Hostel实体的任何属性。 生成的查询是：

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 ?

此查询无效，因为它返回五个Map为空。 FIve地图是因为有五个Hostel行符合条件。我创建了简单的SQL查询，它工作正常所以问题只在这里。

如何强制hibernate获取根Hostel实体的所有属性，只获取3个@ {1}}实体的属性？

修改 我尝试使用User owner，但它在getSessionFactory().getClassMetadata(Hostel.class)中映射枚举时出错。所以我回退到手动列出Hostel属性。现在我的标准查询是：

Hostel

请注意，我删除了// 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); } 结果转换器。这生成了这样的mysql查询：

ALIAS_TO_ENTITY_MAP

在for-each循环中出现这样的错误：

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 ?

此错误表示我在结果列表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) 中没有Hostel类型。 我甚至试图找出结果列表中的元素类别＆＃39; hostels＆＃39;有了这个：

hostels

打印出来：

List hostels = criteria.list();
        System.out.println("firstRow.class=" + hostels.get(0).getClass());

然后我尝试为新的ProjectionList设置firstRow.class=class [Ljava.lang.Object; ，但结果列表＆＃39; hostels＆＃39;是：

ALIAS_TO_ENTITY_MAP

五张空地图。五，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，并且hibernate按预期检索了5个旅馆和5个关联的[{}, {}, {}, {}, {}] 和User owner的图像。

问题是如何阻止hibernate检索关联owner的关联Image实体。最好的方法是只获取相关User owner的3个特定道具。

谢谢！

3 个答案:

答案 0 :(得分：8)

您可以使用直接查询来执行此操作：

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();

生成一个SQL，如：

  

选择hostel0_.id为col_0_0_，user1_.id为col_1_0_，user1_.firstname为col_2_0_，user1_.lastname为col_3_0_，hostel0_.id为id1_0_，hostel0_.name为name2_0_，...，hostel0_.owner_id为user_id4_0_来自宿舍0_左外连接用户user1_ on user1_.id = hostel0_.owner_id

包含来自宿舍的所有字段，仅包含来自用户的必填字段。

使用criteria.list()获得的列表是List<Object[]>，其行为 [ Hostel, Integer, String, String]

您可以使用Criteria获取内容，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。据我所知，不可能获得包含实体（Hostels）的行和来自关联的单独字段（owner.userId，owner.firstName，owner.lastName）。

我能想象的唯一方法就是明确列出旅舍的所有字段：

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")));

你可以使用元数据自动化一点（不要忘记id ...） - 注意：我只使用别名投影以后才能使用包装类，如果你直接使用标量值，你可以安全地省略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();

这样就可以正确生成

  

选择this_.id为y0_，this_.name为y1_，...，this_.user_id为y3_，owner1_.id为y4_，owner1_.firstname为y5_，owner1_.lastname为y6_ from hotels this_ left outer join users owner1_ on this_.user_id = owner1_.id

但是您将无法使用criteria.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP)因为结果集不完全是来自Hostel的字段的图像（即使没有别名）。 实际上，列表是List<Object[]>，其中的行包含Hostel中的所有单个字段，后跟owner中的3个必填字段。

您必须添加一个包含Hostel和其他3个字段的包装类，以便使用AliasToBeanResultTransformer并获取真正的Hostel个对象：

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 ...
}

然后你就可以成功写下：

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hostel.getOwner()为空时，如果有，hostel.getOwner().getId()等于getOwner_id()并且此访问不会生成任何额外查询。但是，对hostel.getOwner()的其他字段，甚至firstName或lastName的任何访问都会生成一个，因为会话中未加载User实体。

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
}

答案 1 :(得分：3)

@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;
    }

HostelWrapper使用AliasToBeanResultTransformer将hibernate结果集映射到实体。

我的最终结论是，当你想在关联上设置投影时，HQL是正确的方法。 使用AliasToBeanResultTransformer，您将绑定属性名称，并且hql是相同的。好处是HQL更容易编写。

答案 2 :(得分：1)

根据我的观察，你无法按照你的要求得到结果。

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")));

请尝试并知道。

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