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去除子查询在JPA标准中产生的冗余连接

数据库问题
2022-01-01

Get rid of redundant joins produced by subqueries in JPA criteria(去除子查询在JPA标准中产生的冗余连接)

本文介绍了去除子查询在JPA标准中产生的冗余连接的处理方法，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

我只需要使用JPA标准执行以下MySQL查询(根据给定的国家名称(在country中)从state_table获取一个州的列表)。 

SELECT state_id, 
       state_name, 
       country_id
FROM   state_table 
WHERE  country_id IN(SELECT country_id 
                     FROM   country 
                     WHERE  country_name = ?)

我编写了以下JPA标准查询。

CriteriaBuilder criteriaBuilder=entityManager.getCriteriaBuilder();
CriteriaQuery<StateTable>criteriaQuery=criteriaBuilder.createQuery(StateTable.class);
Root<StateTable> root = criteriaQuery.from(entityManager.getMetamodel().entity(StateTable.class));

Subquery<Long> subquery = criteriaQuery.subquery(Long.class);
Root<Country> subRoot = subquery.from(Country.class);
subquery.select(subRoot.get(Country_.countryId));

ParameterExpression<String>parameterExpression=criteriaBuilder.parameter(String.class);
subquery.where(criteriaBuilder.equal(subRoot.get(Country_.countryName), parameterExpression));
criteriaQuery.where(criteriaBuilder.in(root.get(StateTable_.country).get(Country_.countryId)).value(subquery));
List<StateTable> list = entityManager.createQuery(criteriaQuery).setParameter(parameterExpression, "India").getResultList();

此条件查询不必要地在生成的SQL查询中生成冗余联接，如下所示。

SELECT t1.state_id, 
       t1.state_name, 
       t1.country_id 
FROM   projectdb.country t0, 
       projectdb.state_table t1 
WHERE  (t0.country_id IN (SELECT t2.country_id 
                           FROM   projectdb.country t2 
                           WHERE  (t2.country_name = ? )) 
         AND (t0.country_id = t1.country_id ))

可以注意到，存在冗余联接AND (t0.country_id = t1.country_id ))。

这是由root.get(StateTable_.countryId).get(Country_.countryId)引起的，root.get(StateTable_.countryId).get(Country_.countryId)意味着在上面给出的条件查询中的以下行中有一个内部联接。在这种情况下，不应出现不必要的情况。

criteriaQuery.where(criteriaBuilder.in(root.get(StateTable_.countryId).get(Country_.countryId)).value(subquery));

如何删除此冗余联接？

我使用的是NikpseLink 2.3.2提供的JPA 2.0。

在这种情况下，与其使用子查询，不如在这两个表之间使用联接来处理，但编写这样的子查询而不使用冗余联接应该是可能的，因为这是一件非常基本的事情。

编辑1：

等效的EXISTS()查询可以按如下方式正常工作。

CriteriaBuilder criteriaBuilder=entityManager.getCriteriaBuilder();
CriteriaQuery<StateTable>criteriaQuery=criteriaBuilder.createQuery(StateTable.class);
Root<StateTable> root = criteriaQuery.from(entityManager.getMetamodel().entity(StateTable.class));
criteriaQuery.select(root);

Subquery<Long> subquery = criteriaQuery.subquery(Long.class);
Root<Country> subRoot = subquery.from(Country.class);
subquery.select(subRoot.get(Country_.countryId));

ParameterExpression<String>parameterExpression=criteriaBuilder.parameter(String.class);
subquery.where(criteriaBuilder.equal(root.get(StateTable_.country), subRoot), criteriaBuilder.equal(subRoot.get(Country_.countryName), parameterExpression));

criteriaQuery.where(criteriaBuilder.exists(subquery));
List<StateTable> list = entityManager.createQuery(criteriaQuery).setParameter(parameterExpression, "India").getResultList();

导致生成以下正确的SQL查询，该查询将被委托给MySQL。

SELECT t0.state_id, 
       t0.state_name, 
       t0.country_id 
FROM   projectdb.state_table t0 
WHERE  EXISTS (SELECT t1.country_id 
               FROM   projectdb.country t1 
               WHERE  ((t0.country_id = t1.country_id) 
                        AND (t1.country_name = ?)))

找不到生成等效IN()查询的方法。

编辑2：

以下JPQL，

SELECT s 
FROM   StateTable s 
WHERE  s.country IN(SELECT c 
                      FROM   Country c 
                      WHERE  c.countryname = :countryName)

生成正确的IN()子查询。

SELECT t0.state_id, 
       t0.state_name, 
       t0.country_id 
FROM   projectdb.state_table t0 
WHERE  t0.country_id IN (SELECT t1.country_id 
                         FROM   projectdb.country t1 
                         WHERE  (t1.country_name = ?))

由此，我可以设想以下条件查询。

CriteriaBuilder criteriaBuilder=entityManager.getCriteriaBuilder();
CriteriaQuery<StateTable>criteriaQuery=criteriaBuilder.createQuery(StateTable.class);
Root<StateTable> root = criteriaQuery.from(entityManager.getMetamodel().entity(StateTable.class));
criteriaQuery.select(root);

Subquery<Country> subquery = criteriaQuery.subquery(Country.class);
Root<Country> subRoot = subquery.from(Country.class);
subquery.select(subRoot);

ParameterExpression<String>parameterExpression=criteriaBuilder.parameter(String.class);
subquery.where(criteriaBuilder.equal(subRoot.get(Country_.countryName), parameterExpression));

criteriaQuery.where(criteriaBuilder.in(root.get(StateTable_.country)).value(subquery));
List<StateTable> list = entityManager.createQuery(criteriaQuery).setParameter(parameterExpression, "India").getResultList();

但它在运行时失败，出现以下异常。

Exception [EclipseLink-6048] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.QueryException
Exception Description: Illegal use of getField() [projectdb.country.country_id] in expression.
Query: ReadAllQuery(referenceClass=StateTable )
    at org.eclipse.persistence.exceptions.QueryException.illegalUseOfGetField(QueryException.java:563)
    at org.eclipse.persistence.expressions.Expression.getField(Expression.java:1739)
    at org.eclipse.persistence.internal.expressions.FunctionExpression.normalize(FunctionExpression.java:476)
    at org.eclipse.persistence.internal.expressions.SQLSelectStatement.normalize(SQLSelectStatement.java:1402)
    at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.buildNormalSelectStatement(ExpressionQueryMechanism.java:549)
    at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.prepareSelectAllRows(ExpressionQueryMechanism.java:1708)
    at org.eclipse.persistence.queries.ReadAllQuery.prepareSelectAllRows(ReadAllQuery.java:785)
    at org.eclipse.persistence.queries.ReadAllQuery.prepare(ReadAllQuery.java:716)
    at org.eclipse.persistence.queries.DatabaseQuery.checkPrepare(DatabaseQuery.java:661)
    at org.eclipse.persistence.queries.ObjectLevelReadQuery.checkPrepare(ObjectLevelReadQuery.java:888)
    at org.eclipse.persistence.queries.DatabaseQuery.checkPrepare(DatabaseQuery.java:613)
    at org.eclipse.persistence.queries.DatabaseQuery.execute(DatabaseQuery.java:867)
    at org.eclipse.persistence.queries.ObjectLevelReadQuery.execute(ObjectLevelReadQuery.java:1114)
    at org.eclipse.persistence.queries.ReadAllQuery.execute(ReadAllQuery.java:402)
    at org.eclipse.persistence.queries.ObjectLevelReadQuery.executeInUnitOfWork(ObjectLevelReadQuery.java:1202)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.internalExecuteQuery(UnitOfWorkImpl.java:2894)
    at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1797)
    at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1779)
    at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1744)
    at org.eclipse.persistence.internal.jpa.QueryImpl.executeReadQuery(QueryImpl.java:258)
    at org.eclipse.persistence.internal.jpa.QueryImpl.getResultList(QueryImpl.java:468)
    at client.beans.ProductDetailsBean.test(ProductDetailsBean.java:139)
    at client.beans.ProductDetailsBean.getProductList(ProductDetailsBean.java:119)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1081)
    at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1153)
    at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:4695)
    at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:630)
    at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
    at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
    at org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:46)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
    at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
    at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:582)
    at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doCall(SystemInterceptorProxy.java:163)
    at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:140)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
    at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
    at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:369)
    at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:4667)
    at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:4655)
    at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
    at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:88)
    at $Proxy482.getProductList(Unknown Source)
    at client.bean.ProductDetailsManagedBean.load(ProductDetailsManagedBean.java:59)
    at org.primefaces.component.datagrid.DataGrid.loadLazyData(DataGrid.java:144)
    at org.primefaces.component.datagrid.DataGridRenderer.encodeMarkup(DataGridRenderer.java:54)
    at org.primefaces.component.datagrid.DataGridRenderer.encodeEnd(DataGridRenderer.java:47)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:74)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:57)
    at org.primefaces.component.panel.PanelRenderer.encodeContent(PanelRenderer.java:204)
    at org.primefaces.component.panel.PanelRenderer.encodeMarkup(PanelRenderer.java:121)
    at org.primefaces.component.panel.PanelRenderer.encodeEnd(PanelRenderer.java:58)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1864)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:176)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
    at org.primefaces.renderkit.CoreRenderer.renderChild(CoreRenderer.java:70)
    at org.primefaces.renderkit.CoreRenderer.renderChildren(CoreRenderer.java:57)
    at org.primefaces.component.layout.LayoutUnitRenderer.encodeEnd(LayoutUnitRenderer.java:51)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1864)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1860)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1860)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1860)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:461)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
    at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
    at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:344)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
    at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:70)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:316)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
    at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
    at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
    at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
    at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
    at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
    at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
    at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
    at java.lang.Thread.run(Thread.java:722)

我看不到此异常背后的任何原因。

编辑3：

在最新版本中相同的条件查询--出现异常而失败的那个，在Hibernate(4.2.7最终版)提供的JPA上运行正常，根本不需要修改，在不同的项目中具有完全相同的表关系。

它生成以下正确的SQL查询。

SELECT
    statetable0_.state_id as state_id1_24_,
    statetable0_.country_id as country_3_24_,
    statetable0_.state_name as state_na2_24_ 
FROM
    social_networking.state_table statetable0_ 
WHERE
    statetable0_.country_id IN (
        SELECT
            country1_.country_id 
        FROM
            social_networking.country country1_ 
        WHERE
            country1_.country_name=?
    )

因此，在NikpseLink的幕后应该会发生一些不可靠的事情。

我是否应该安全地假设这是Criteria API中的NikpseLink中的疏忽？

编辑4：

如上所述使用EXISTS()也会产生冗余连接，如果查询语句颠倒过来，

SELECT * 
FROM   country c 
WHERE  EXISTS (SELECT s.country_id 
               FROM   state_table s 
               WHERE  s.country_id = c.country_id 
                      AND s.state_name = 'desired_state_name')

Hibernate提供的JPA(我当前使用的是4.2.7最终版)生成查询语句，这是我们通常在没有这种冗余联接的情况下所期望的。

这是一个非常基本的查询，很难相信这是NikpseLink中的疏忽。在我看来，我一定是做错了什么，一定是遗漏了一些显而易见的、非常基本的东西。请澄清。

我最近已将NikpseLink升级到其最新版本2.5.1，并安装了JPA 2.1。

长话短说：引用root.get("property1").get("propery2InAnotherRelatedEntity")这样的实体中的嵌套属性总是会导致生成多余的联接，这通常不应该发生。

请原谅我，如果我做了这么多修改，但我不得不…：)

JPA

示例中的冗余联接是由不正确的推荐答案标准查询构造产生的，而不是由其中的子查询产生的。所以这个问题的题目真的没有多大意义。

要消除冗余联接，您只需正确构建条件。事实上，编辑2中的条件查询是问题开头的原始SQL查询到JPA条件语言的正确转换，不应该产生任何多余的联接。您使用Hibernate进行的实验证实了这一点。而你得到的QueryException绝对是一个NikpseLink的错误。我建议您将其报告给NikpseLink：https://wiki.eclipse.org/EclipseLink/Bugs的开发人员。

但实际上，这里根本不需要子查询，如果使用正确，连接通常不是坏事，所以我建议用这个完全等价但更简洁的查询来替换SQL查询：

SELECT state_id,
       state_name,
       s.country_id
FROM   state_table s, country c
WHERE  s.country_id = c.country_id AND country_name = ?

它到条件查询的翻译也简单明了得多(肯定不会混淆NikpseLink：))：

CriteriaBuilder criteriaBuilder =
    entityManager.getCriteriaBuilder();

CriteriaQuery<StateTable> criteriaQuery =
    criteriaBuilder.createQuery(StateTable.class);

Root<StateTable> root = criteriaQuery.from(StateTable.class);
ParameterExpression<String> parameterExpression =
    criteriaBuilder.parameter(String.class);

criteriaQuery.where(criteriaBuilder.equal(
    root.get(StateTable_.country).get(Country_.countryName),
    parameterExpression));

List<StateTable> list = entityManager.createQuery(criteriaQuery)
    .setParameter(parameterExpression, "India").getResultList();

并且在MySQL中的性能不会比原始版本差。

这篇关于去除子查询在JPA标准中产生的冗余连接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编程学习网！

本文标题为：去除子查询在JPA标准中产生的冗余连接

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