org.hibernate.AnnotationException: No identifier specified for entity: com.example1.demo1.Entity.User错误

最近在公司带人，他们问我的问题在这里也顺便总结下。

此项目为SpringDataJpa项目。

出现的错误如下：

Caused by: org.hibernate.AnnotationException: No identifier specified for entity: com.example1.demo1.Entity.User
    at org.hibernate.cfg.InheritanceState.determineDefaultAccessType(InheritanceState.java:266) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.hibernate.cfg.InheritanceState.getElementsToProcess(InheritanceState.java:211) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:731) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.hibernate.boot.model.source.internal.annotations.AnnotationMetadataSourceProcessorImpl.processEntityHierarchies(AnnotationMetadataSourceProcessorImpl.java:249) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.hibernate.boot.model.process.spi.MetadataBuildingProcess$1.processEntityHierarchies(MetadataBuildingProcess.java:222) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:265) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:861) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:888) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:57) ~[spring-orm-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:390) ~[spring-orm-5.0.6.RELEASE.jar:5.0.6.RELEASE]

解决办法：

在此Entity类上添加注解：@MappedSuperclass方可解决。

@MappedSuperclass
@Entity
public class User {

    //主键id，自增
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    private String username;

    private String password;

    private String email;

    private Date createtime;

    private Date updatetime;

    private int age;

}

以后有问题将会继续更新