"org.hibernate.AnnotationException: No identifier specified for entity"異常分析

環境設置

Spring Data JPA， Hibernate
Spring Boot 2.1.13.RELEASE

異常信息：

異常信息如下：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is org.hibernate.AnnotationException: No identifier specified for entity: org.spb.data.dao.entity.UserEntity
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1771) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1105) ~[spring-context-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867) ~[spring-context-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.1.13.RELEASE.jar:2.1.13.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:744) [spring-boot-2.1.13.RELEASE.jar:2.1.13.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:391) [spring-boot-2.1.13.RELEASE.jar:2.1.13.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:312) [spring-boot-2.1.13.RELEASE.jar:2.1.13.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.1.13.RELEASE.jar:2.1.13.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1204) [spring-boot-2.1.13.RELEASE.jar:2.1.13.RELEASE]
	at org.spb.data.UserLoginApplication.main(UserLoginApplication.java:14) [classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_192]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_192]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_192]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_192]
	at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.1.13.RELEASE.jar:2.1.13.RELEASE]
Caused by: org.hibernate.AnnotationException: No identifier specified for entity: org.spb.data.dao.entity.UserEntity
	at org.hibernate.cfg.InheritanceState.determineDefaultAccessType(InheritanceState.java:266) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.hibernate.cfg.InheritanceState.getElementsToProcess(InheritanceState.java:211) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:775) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.hibernate.boot.model.source.internal.annotations.AnnotationMetadataSourceProcessorImpl.processEntityHierarchies(AnnotationMetadataSourceProcessorImpl.java:250) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.hibernate.boot.model.process.spi.MetadataBuildingProcess$1.processEntityHierarchies(MetadataBuildingProcess.java:231) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:274) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:1215) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1246) ~[hibernate-core-5.3.15.Final.jar:5.3.15.Final]
	at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) ~[spring-orm-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:391) ~[spring-orm-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:378) ~[spring-orm-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1830) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1767) ~[spring-beans-5.1.14.RELEASE.jar:5.1.14.RELEASE]
	... 21 common frames omitted

問題分析

從異常信息分析可知，缺乏唯一標識，應該主鍵之類的缺失。
UserEntity.java定義如下：

@Entity
@Table(name="auth_user")
@Data@EqualsAndHashCode(callSuper=true)
public class UserEntity extends BaseEntity {
	private static final long serialVersionUID = 8413191100461926897L;

	@Column
	private String name;
	
	@Column
	private String password;
	
	//Role List
	@Column
	private List<String> roles;
}

BaseEntity.java定義如下：

package org.spb.data.dao.base;

import java.io.Serializable;
import java.time.LocalDateTime;
import java.util.Date;

import javax.persistence.Column;
import javax.persistence.EntityListeners;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import lombok.Data;

@Data
public abstract class BaseEntity implements Serializable {
	private static final long serialVersionUID = -5777041700442398469L;

	@Id
	@GeneratedValue
	private Long id;
	
    //..............
    //樂觀鎖
    @Version
    private Long version;
}

在BaseEntity明明定義了@Id主鍵的，爲什麼不啓作用呢？那問題應該就在這裏。
經過一份查找之後得知，這裏需要增加一個將當前類標註爲：

@MappedSuperclass

問題解決

將@MappedSuperclass放置到BaseEntity之上即可解決問題。
其在官方文檔中定義如下：

Designates a class whose mapping information is applied to the entities that inherit from it. A mapped superclass  has no separate table defined for it.  
A class designated with the <code>MappedSuperclass</code>  annotation can be mapped in the same way as an entity except that the mappings will apply only to its subclasses since no table  exists for the mapped superclass itself. When applied to the  subclasses the inherited mappings will apply in the context  of the subclass tables.

其核心意思是：其做基本，無實際的表與之對應。