Failed to run CommandLineRunner (Spring Boot)

Question

Whenever I try to run my code I get this error here:

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:809) ~[spring-boot-2.4.4.jar:2.4.4]
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:790) ~[spring-boot-2.4.4.jar:2.4.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:333) ~[spring-boot-2.4.4.jar:2.4.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1313) ~[spring-boot-2.4.4.jar:2.4.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1302) ~[spring-boot-2.4.4.jar:2.4.4]
    at de.hdm_stuttgart.finance_manager.FinanceManagerApplication.main(FinanceManagerApplication.java:24) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[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:567) ~[na:na]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.4.4.jar:2.4.4]
Caused by: org.springframework.dao.InvalidDataAccessApiUsageException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : de.hdm_stuttgart.finance_manager.model.Expenses.category -> de.hdm_stuttgart.finance_manager.model.Category; nested exception is java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : de.hdm_stuttgart.finance_manager.model.Expenses.category -> de.hdm_stuttgart.finance_manager.model.Category
    at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:371) ~[spring-orm-5.3.5.jar:5.3.5]
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:235) ~[spring-orm-5.3.5.jar:5.3.5]
    at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:566) ~[spring-orm-5.3.5.jar:5.3.5]
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:743) ~[spring-tx-5.3.5.jar:5.3.5]
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:711) ~[spring-tx-5.3.5.jar:5.3.5]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:654) ~[spring-tx-5.3.5.jar:5.3.5]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:407) ~[spring-tx-5.3.5.jar:5.3.5]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119) ~[spring-tx-5.3.5.jar:5.3.5]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.5.jar:5.3.5]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137) ~[spring-tx-5.3.5.jar:5.3.5]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.5.jar:5.3.5]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:174) ~[spring-data-jpa-2.4.6.jar:2.4.6]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.5.jar:5.3.5]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.5.jar:5.3.5]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.5.jar:5.3.5]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.5.jar:5.3.5]
    at jdk.proxy4/jdk.proxy4.$Proxy82.save(Unknown Source) ~[na:na]
    at de.hdm_stuttgart.finance_manager.FinanceManagerApplication.lambda$demo$0(FinanceManagerApplication.java:31) ~[classes/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:806) ~[spring-boot-2.4.4.jar:2.4.4]
    ... 10 common frames omitted
Caused by: java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : de.hdm_stuttgart.finance_manager.model.Expenses.category -> de.hdm_stuttgart.finance_manager.model.Category
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:151) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:181) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:188) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1366) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:453) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.internal.SessionImpl.flushBeforeTransactionCompletion(SessionImpl.java:3212) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.internal.SessionImpl.beforeTransactionCompletion(SessionImpl.java:2380) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.beforeTransactionCompletion(JdbcCoordinatorImpl.java:447) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.beforeCompletionCallback(JdbcResourceLocalTransactionCoordinatorImpl.java:183) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.access$300(JdbcResourceLocalTransactionCoordinatorImpl.java:40) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:281) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:101) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:562) ~[spring-orm-5.3.5.jar:5.3.5]
    ... 26 common frames omitted
Caused by: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : de.hdm_stuttgart.finance_manager.model.Expenses.category -> de.hdm_stuttgart.finance_manager.model.Category
    at org.hibernate.engine.spi.CascadingActions$8.noCascade(CascadingActions.java:379) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:167) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.event.internal.AbstractFlushingEventListener.cascadeOnFlush(AbstractFlushingEventListener.java:159) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.event.internal.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:149) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:82) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:39) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:93) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    at org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1362) ~[hibernate-core-5.4.29.Final.jar:5.4.29.Final]
    ... 35 common frames omitted

This is my start application:

package de.hdm_stuttgart.finance_manager;

import de.hdm_stuttgart.finance_manager.model.Category;
import de.hdm_stuttgart.finance_manager.model.Expense;
import de.hdm_stuttgart.finance_manager.model.PaymentMethod;
import de.hdm_stuttgart.finance_manager.repository.ExpenseRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import java.util.Date;

@SpringBootApplication
public class FinanceManagerApplication {

    private static final Logger log = LoggerFactory.getLogger(FinanceManagerApplication.class);

    public static void main(String[] args) {
        SpringApplication.run(FinanceManagerApplication.class, args);
    }

    @Bean
    public CommandLineRunner demo(ExpenseRepository repo) {
        return (args) -> {
            log.info("Creating expense entities...");
            repo.save(new Expense(new Date(), 28.99, "Hai Vu", "Essen", new Category("Leisure"), PaymentMethod.CASH));

        };
    }

}

My friends has the exact same code but it works for them but not for me and we do not know what the reason is. The configuration is all the same, but why is it failing to run the CommandLineRunner?

EDIT:

So something wrong is with my Expense class or ExpenseRepository, but I still don't know why. With other repository it works and also I tried a new project with a PersonRepository. But always the ExpenseRepository fail. I also renamed it but always get this Exception...

This is my Expense Model

package de.hdm_stuttgart.finance_manager.model;

import javax.persistence.*;
import java.math.BigDecimal;
import java.util.Date;

@Entity
public class Expense {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @Temporal(TemporalType.DATE)
    private Date date;
    private BigDecimal amount;
    private String receiver;
    private String purpose;

    @ManyToOne
    private Category category;

    @Enumerated(EnumType.STRING)
    private PaymentMethod paymentMethod;

    public Expense(){}

    public Expense(Date date, BigDecimal amount, String receiver, String purpose, Category category, PaymentMethod paymentMethod) {
        this.date = date;
        this.amount = amount;
        this.receiver = receiver;
        this.purpose = purpose;
        this.category = category;
        this.paymentMethod = paymentMethod;
    }
}

And my ExpenseRepository is just plain like this

package de.hdm_stuttgart.finance_manager.repository;

import de.hdm_stuttgart.finance_manager.model.Expense;
import org.springframework.data.repository.CrudRepository;

public interface ExpenseRepository extends CrudRepository<Expense, Long> {
}

Answer 1

Try removing the ExpenseRepository and start the app. If it works, then ExpenseRepository related package scanning or Entity associated to that Repository scanning is not loading properly.