Spring JpaRepository using generic entity

Question

I'm trying to implement a generic DAO like this to use it with X Entities quite similar (id, code, description):

@Repository
public interface GenericDao<T> extends JpaRepository<T, Long> {

    T findByCode(String code);
    T findById(Long id);
}

One of my Entities is like this:

@Getter
@Setter
@Entity
@Table(name = "TEST")
public class Test {...}

I've got a Service where I need to use the Dao:

@Service
public class TestServiceImpl implements TestService {

    private GenericDao<Test> testDao;

    @Autowired
    public TestServiceImpl(GenericDao<Test> testDao) {
        this.testDao = testDao;
    }
}

When I start my application using SpringBoot the application doesn't start and the error is:

Caused by: org.springframework.beans.factory.BeanCreationException: Error     creating bean with name 'genericDao': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Not an managed type: class java.lang.Object
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1574)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1127)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1044)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:813)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741)
... 23 more
Caused by: java.lang.IllegalArgumentException: Not an managed type: class java.lang.Object
at org.hibernate.jpa.internal.metamodel.MetamodelImpl.managedType(MetamodelImpl.java:219)
at org.springframework.data.jpa.repository.support.JpaMetamodelEntityInformation.<init>(JpaMetamodelEntityInformation.java:68)
at org.springframework.data.jpa.repository.support.JpaEntityInformationSupport.getMetadata(JpaEntityInformationSupport.java:67)
at org.springframework.data.jpa.repository.support.JpaRepositoryFactory.getEntityInformation(JpaRepositoryFactory.java:145)
at org.springframework.data.jpa.repository.support.JpaRepositoryFactory.getTargetRepository(JpaRepositoryFactory.java:89)
at org.springframework.data.jpa.repository.support.JpaRepositoryFactory.getTargetRepository(JpaRepositoryFactory.java:69)
at org.springframework.data.repository.core.support.RepositoryFactorySupport.getRepository(RepositoryFactorySupport.java:172)
at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.initAndReturn(RepositoryFactoryBeanSupport.java:239)
at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.afterPropertiesSet(RepositoryFactoryBeanSupport.java:225)
at org.springframework.data.jpa.repository.support.JpaRepositoryFactoryBean.afterPropertiesSet(JpaRepositoryFactoryBean.java:92)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1633)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1570)
... 34 more

Answer 1

You can't do this. Spring trying to create your repository on start, not on autowiring moment. But Spring absolutely has no idea, what kind of generic param it should to use. So it is trying to instantiate this repository with Object. But Object is not entity, so you get corresponding error.

Conclusion: you repository must be of specific type, but not generic.