Spring Annotation Object Mapping generic class relationship - spring

Question

I use Spring to store objects from the annotation based Object Mapping in a Neo4j database.
I have a generic class(InformationMutable) which contains as class attribute a list of another class(InformationEntry) of the same generic data type - private List<InformationEntry<T>> entries = new ArrayList<>();.
Full InformationMutable class:
package de.skillkiller.project.entity;
import lombok.*;
import org.springframework.data.neo4j.core.schema.Node;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
#EqualsAndHashCode(callSuper = true)
#Node
#Data
#ToString(callSuper = true)
#NoArgsConstructor
#AllArgsConstructor
public class InformationMutable<T extends Serializable> extends Information {
private List<InformationEntry<T>> entries = new ArrayList<>();
public void addEntry(T entry) {
entries.add(new InformationEntry<>(entry));
}
public void removeEntry(InformationEntry<T> entry) {
entries.remove(entry);
}
}
The goal is to have an object where in the list is only objects of the other class but with the same datatype in it. The InformationEntry class extends the datatype with uniform create and update dates.
Other required classes:
InformationEntry:
package de.skillkiller.project.entity;
import lombok.*;
import org.springframework.data.neo4j.core.schema.Node;
import java.io.Serializable;
#EqualsAndHashCode(callSuper = true)
#Node
#Data
#ToString(callSuper = true)
#NoArgsConstructor
#AllArgsConstructor
public class InformationEntry<T extends Serializable> extends BasicNode{
private T entry;
}
Information:
package de.skillkiller.project.entity;
import lombok.*;
import org.springframework.data.neo4j.core.schema.Node;
#EqualsAndHashCode(callSuper = true)
#Node
#Data
#ToString(callSuper = true)
#NoArgsConstructor
#AllArgsConstructor
public abstract class Information extends BasicNode{
private String information;
}
BasicNode:
package de.skillkiller.project.entity;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.data.annotation.CreatedDate;
import org.springframework.data.annotation.LastModifiedDate;
import org.springframework.data.neo4j.core.schema.GeneratedValue;
import org.springframework.data.neo4j.core.schema.Id;
import org.springframework.data.neo4j.core.support.DateLong;
import java.util.Date;
#Data
#AllArgsConstructor
#NoArgsConstructor
public abstract class BasicNode {
#Id
#GeneratedValue
private Long id;
#DateLong
#LastModifiedDate
private Date changedAt = new Date();
#DateLong
#CreatedDate
private Date enteredAt = new Date();
}
InformationRepository:
package de.skillkiller.project.repository;
import de.skillkiller.project.entity.Information;
import org.springframework.data.neo4j.repository.Neo4jRepository;
public interface InformationRepository extends Neo4jRepository<Information, Long> {
}
Creation Process:
InformationMutable<Integer> informationMutable1 = new InformationMutable<>();
informationMutable1.addEntry(5);
informationMutable1.addEntry(15);
informationMutable1.setInformation("Test");
informationRepository.save(informationMutable1);
If I now create an object from the class InformationMutable, add values to the list and want to save it, I get the following error message:
ava.lang.IllegalStateException: Failed to execute CommandLineRunner
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:807) ~[spring-boot-2.4.2.jar:2.4.2]
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:788) ~[spring-boot-2.4.2.jar:2.4.2]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:333) ~[spring-boot-2.4.2.jar:2.4.2]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1311) ~[spring-boot-2.4.2.jar:2.4.2]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1300) ~[spring-boot-2.4.2.jar:2.4.2]
at de.skillkiller.project.ProjectApplication.main(ProjectApplication.java:19) ~[classes/:na]
Caused by: java.lang.NullPointerException: Cannot invoke "org.springframework.data.neo4j.core.mapping.Neo4jPersistentEntity.isNew(Object)" because "targetNodeDescription" is null
at org.springframework.data.neo4j.core.Neo4jTemplate.lambda$processNestedRelations$16(Neo4jTemplate.java:495) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at org.springframework.data.mapping.model.BasicPersistentEntity.doWithAssociations(BasicPersistentEntity.java:387) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.neo4j.core.Neo4jTemplate.processNestedRelations(Neo4jTemplate.java:452) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at org.springframework.data.neo4j.core.Neo4jTemplate.lambda$processNestedRelations$16(Neo4jTemplate.java:518) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at org.springframework.data.mapping.model.BasicPersistentEntity.doWithAssociations(BasicPersistentEntity.java:387) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.neo4j.core.Neo4jTemplate.processNestedRelations(Neo4jTemplate.java:452) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at org.springframework.data.neo4j.core.Neo4jTemplate.processRelations(Neo4jTemplate.java:442) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at org.springframework.data.neo4j.core.Neo4jTemplate.saveImpl(Neo4jTemplate.java:254) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at org.springframework.data.neo4j.core.Neo4jTemplate.save(Neo4jTemplate.java:225) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at org.springframework.data.neo4j.repository.support.SimpleNeo4jRepository.save(SimpleNeo4jRepository.java:131) ~[spring-data-neo4j-6.0.3.jar:6.0.3]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]
at org.springframework.data.repository.core.support.RepositoryMethodInvoker$RepositoryFragmentMethodInvoker.lambda$new$0(RepositoryMethodInvoker.java:289) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.repository.core.support.RepositoryComposition$RepositoryFragments.invoke(RepositoryComposition.java:524) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.repository.core.support.RepositoryComposition.invoke(RepositoryComposition.java:285) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.repository.core.support.RepositoryFactorySupport$ImplementationMethodExecutionInterceptor.invoke(RepositoryFactorySupport.java:531) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.3.jar:5.3.3]
at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:156) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:131) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.3.jar:5.3.3]
at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:80) ~[spring-data-commons-2.4.3.jar:2.4.3]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.3.jar:5.3.3]
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123) ~[spring-tx-5.3.3.jar:5.3.3]
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388) ~[spring-tx-5.3.3.jar:5.3.3]
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119) ~[spring-tx-5.3.3.jar:5.3.3]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.3.jar:5.3.3]
at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137) ~[spring-tx-5.3.3.jar:5.3.3]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.3.jar:5.3.3]
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.3.jar:5.3.3]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.3.jar:5.3.3]
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.3.jar:5.3.3]
at com.sun.proxy.$Proxy67.save(Unknown Source) ~[na:na]
at de.skillkiller.project.ProjectApplication.lambda$demo$0(ProjectApplication.java:57) ~[classes/:na]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:804) ~[spring-boot-2.4.2.jar:2.4.2]
... 5 common frames omitted
Nevertheless, is it somehow possible with Spring and Neo4j to store such a generic construct and read it out again?

Answer 1

The problem with your setting is that the InformationMutable declares a generic field that is seen by SDN as any other legit #Node annotated entity.
As a consequence SDN wants to create something like
(:Information:InformationMutable) -[:ENTRIES]-> (:InformationEntry) -[:ENTRY] -> (generic entry)
It does not see the generic field as a possible property and it cannot because the definition of the Integer type is done during runtime.
The green nodes on the right side are for example other real #Node entities that you could use and that contain a fixed Integer field, for example.