休眠自定义多个字段选择

Question

我们有几种型号，如下所示。

@Entity
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Person {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public int id;

    @Column(nullable = false, columnDefinition = "text")
    public String name;

    @Column(nullable = false, unique = true)
    public long ssid;

    @Column(nullable = false)
    public int age;

    @Column(nullable = false)
    public long registration;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "person")
    @Cascade(CascadeType.ALL)
    public List<Car> cars;


}

车型

@Entity
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Car {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public int id;

    @Column(nullable = false, columnDefinition = "text")
    private String name;

    @Column(nullable = false,  unique = true)
    public String plateNumber;

    @ManyToOne(fetch = FetchType.LAZY)
    public Person person;

    @ManyToOne(fetch = FetchType.LAZY)
    public Fabric fabric;

}

面料型号

@Entity
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Fabric {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public int id;


    @Column(nullable = false, columnDefinition = "text")
    public String name;


    @OneToMany(fetch = FetchType.LAZY, mappedBy = "fabric")
    @Cascade(CascadeType.ALL)
    public List<Car> cars;
}

问题是，我们在不同的模块上只使用模型的 一些 属性。当我们调用简单类型的属性时是可以的，但是当查询这样的东西时；

session.createQuery("select name, cars from Person order by registration desc ");

我们得到错误。有人可以帮忙吗？

   org.springframework.web.util.NestedServletException: Request processing failed; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.SQLGrammarException: could not extract ResultSet
        org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:982)
        org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
        org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
        org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
        org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
        org.apache.logging.log4j.web.Log4jServletFilter.doFilter(Log4jServletFilter.java:71)

org.hibernate.exception.SQLGrammarException: could not extract ResultSet
    org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:63)
    org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
    org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:111)
    org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:97)
    org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:79)
    org.hibernate.loader.Loader.getResultSet(Loader.java:2123)
    org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1911)
    org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1887)
    org.hibernate.loader.Loader.doQuery(Loader.java:932)
    org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:349)
    org.hibernate.loader.Loader.doList(Loader.java:2615)
    org.hibernate.loader.Loader.doList(Loader.java:2598)
    org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2430)
    org.hibernate.loader.Loader.list(Loader.java:2425)
    org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:502)
    org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:370)
    org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:216)
    org.hibernate.internal.SessionImpl.list(SessionImpl.java:1481)
    org.hibernate.query.internal.AbstractProducedQuery.doList(AbstractProducedQuery.java:1441)
    org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1410)
    org.hibernate.Query.getResultList(Query.java:427)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:333)
    org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
    org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
    org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282)
    org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213)
    com.sun.proxy.$Proxy88.getAllPostOverview(Unknown Source)
    jarvis.api.story.PostController.getAllPostOverviews(PostController.java:51)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:220)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:134)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.apache.logging.log4j.web.Log4jServletFilter.doFilter(Log4jServletFilter.java:71)

Answer 1

不要将cars 指定为查询中的字段。

尝试添加 LEFT JOIN FETCH 子句，关联集合的 Person 实体将在单个查询中加载：

SELECT p.name FROM Person p LEFT JOIN FETCH p.cars ORDER BY p.registration DESC

Answer 2

JPA 不支持按照您的要求进行操作，至少不支持您尝试采用的路径。但是如果你从Car的角度来看待问题，你就可以。

SELECT c, c.person.name FROM Car c ORDER BY c.person.registration DESC

如果您想将此结果集自动填充到值对象中，您可以使用 SELECT NEW 语法或使用 JPA CriteriaBuilder#construct 方法。

SELECT NEW MyValueObject( c, c.person.name )
FROM Car c 
ORDER BY c.person.registration DESC

然后，您可以将 List<MyValueObject> 与 Java Stream API 结合使用，并根据需要在内存中对结果进行分组。

只要明白你得到的结果集包含：

• Car 实例
• 包含Person 名称值的String 实例。

更新

要构建关联Car 的映射，我可能会添加将c.person.id 作为另一个构造函数参数传递给MyValueObject，以防遇到两个同名的人的情况。

List<MyValueObject> queryResults = query.getResultList();
List<List<MyValueObject>> groupedResults = queryResults
  .stream()
  .collect( Collectors.groupingBy( MyValueObject::getPersonId ) )
  .values();

groupedResults 中的每个条目都是与给定 Person 相关联的 Car 实例列表，这些实例封装为 MyValueObject 实例。

Answer 3

你可以试试这个……

session.createQuery("Select ps.name from Person as ps JOIN FETCH ps.cars ORDER BY ps.registration DESC");