使用通用实体的Spring JpaRepository

Question

我正在尝试实现这样的通用DAO，以将其与X实体（ID，代码，描述）非常相似：

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

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

我的实体之一是这样的：

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

我有一个需要使用Dao的服务：

@Service
public class TestServiceImpl implements TestService {

    private GenericDao<Test> testDao;

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

当我使用SpringBoot启动我的应用程序时，该应用程序无法启动，并且错误是：

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

你做不到 Spring尝试在start而不是自动装配时创建存储库。但是Spring绝对不知道应该使用哪种通用参数。因此，它正在尝试使用实例化此存储库Object。但Object不是实体，因此会出现相应的错误。

结论：您的存储库必须为特定类型，但不能为通用类型。

Answer 2

您可以通过一些调整来完成您想要完成的任务。

不要用 @Repository 标记 GenericDao 并按原样使用它，而是使用@NoRepositoryBean注释。正如 JavaDocs 所说，Spring JPA 将尝试初始化附加到 JpaRepository 的任何内容，但 @NoRepositoryBean 允许您创建中间扩展，这些扩展不会被初始化，而您的真实存储库可以从中扩展。您只需确保实现 GenericDao 类的任何内容确实为 T 提供参数。

这意味着您还必须实现 GenericDao 的扩展，该扩展实际上将具有 @Repository 注释，并且您在服务中使用这些 daos 代替泛型。所以你的代码将如下所示：

通用道：

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

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

TestDao，您将添加一个新类，它是参数化实现：

@Repository
public interface TestDao extends GenericDao<Test> {

}

和服务：

@Service
public class TestServiceImpl implements TestService {

    private TestDao testDao;

    @Autowired
    public TestServiceImpl(TestDao testDao) {
        this.testDao = testDao;
    }
}