Query Method NullPointerException on List iteration

#1

Hello,

i'm new to ObjectDB and want to create a query which sums up the product categories of a supplier.

Table Supplier:

supplierId   supplierName address List<Product> products

Table Product:

ProductId productName Price ProductCategory categoriy Supplier supplier

Table ProductCategory:

categoryId categoryName

 

Expected query outcome:

SupplierName Category1_Count Category2_Count
Supplier1         5 13
Supplier2 3 7

 

I tried to do this with a query method:

select s.supplierName, s.countCategory("category1") as Category1, s.countCategory("category2") as Category2
       from Supplier s
       group by s.supplierName

Code:

public int countCategory(String categoryName) {
    int count = 0;
    for (Product p : products) {
        if (p.getCategory().getCategoryName().equals(categoryName)) {
            count++;
        }
    }
    return count;
}

 

Problem: I get a NullPointerException on List<Product> products.

When running a Select s from Supplier s, the product lists are there, so why can i not access the product list in java code?

#2

It is unclear from the question where exactly NullPointerException is thrown.

Try running the query in the Explorer. Do you get results?

If you cannot find the cause, you may post a full minimal program that demonstrates the exception, following the format in the posting instructions.

ObjectDB Support
ObjectDB - Fast Object Database for Java (JPA/JDO)
#3

Hello,

thanks for the quick answer!

 

The NullPointerException is thrown

in Supplier class

in method countCategory(String category) when trying to iterate over the product list:

for (Product p : products) { // code.. }

 

All suppliers have a list of products, so it doesn't make sense that it is null.

 

Unfortunately i can't run the query in the explorer, because it says that the method doesn't exist.

I tried adding the classpath in the explorer settings, but the error remains..

 

Stack Trace:

java.lang.NullPointerException: null
    at com.bi.objectDB.core.entities.Supplier.countCategory(Supplier.java:59) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]
    at com.objectdb.o.MCN.l(MCN.java:269) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.QUN.ZO(QUN.java:687) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.PRG.d(PRG.java:800) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.PRG.h(PRG.java:724) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.PRG.g(PRG.java:560) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.QRM.ZU(QRM.java:287) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.MST.ZU(MST.java:1019) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.WRA.ZU(WRA.java:313) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.WSM.ZU(WSM.java:117) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.QRR.k(QRR.java:260) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.o.QRR.i(QRR.java:154) ~[objectdb-2.8.2.jar:na]
    at com.objectdb.jpa.JpaQuery.getResultList(JpaQuery.java:721) ~[objectdb-2.8.2.jar:na]
    at org.springframework.data.jpa.repository.query.JpaQueryExecution$CollectionExecution.doExecute(JpaQueryExecution.java:126) ~[spring-data-jpa-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:88) ~[spring-data-jpa-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:154) ~[spring-data-jpa-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:142) ~[spring-data-jpa-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor$QueryMethodInvoker.invoke(QueryExecutorMethodInterceptor.java:195) ~[spring-data-commons-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:152) ~[spring-data-commons-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:130) ~[spring-data-commons-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:80) ~[spring-data-commons-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:366) ~[spring-tx-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:118) ~[spring-tx-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139) ~[spring-tx-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:149) ~[spring-data-jpa-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at com.sun.proxy.$Proxy80.findCategoryCount(Unknown Source) ~[na:na]
    at com.bi.objectDB.core.logic.SupplierInformationService.findCategoryCount(SupplierInformationService.java:37) ~[classes/:na]
    at com.bi.objectDB.inbound.SupplierController.findCategoryCount(SupplierController.java:41) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:879) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) ~[na:na]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.35.jar:9.0.35]
    at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]
#4

The relevant Java code that produces the products results is missing in your post.

Is it possible that you close the database or the connection (EntityManager) before using the results?

A full runnable (but minimal, one class) program will help!

ObjectDB Support
ObjectDB - Fast Object Database for Java (JPA/JDO)

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