java - is-hibernate 中的关系

Question

我在 hibernate 中尝试 Is-A 关系的基本示例，但出现错误。

我创建了 3 个 Employee 类的子类

1. SE员工
2. 员工
3. 一名员工

并使用 (joined-subclass ) 标签建立关系。

在此之前，我尝试了使用 (sub-class) 标签的相同示例，它工作得很好，但现在显示了使用 (joined-subclass) 错误。 除了 xml 标签，我没有改变任何东西。 不知道我在这里做错了什么。

mysql.cfg.xml

 <!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    <hibernate-configuration>
    <session-factory>
     <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernatedata</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password">root</property>
    <property name="hibernate.connection.pool_size">10</property>
    <property name="show_sql">true</property>
    <property name="format_sql">true</property>
    <property name="hbm2ddl.auto">update</property>

    <mapping resource="resources/employee.hbm.xml"/>
    </session-factory>
    </hibernate-configuration>

员工.hbm.xml

<joined-subclass name="beans.SEmployee" table="semployee" extends="beans.Employee">
<key column="id"></key>
<property name="tool"></property>
</joined-subclass>

<joined-subclass name="beans.HEmployee" table="hemployee" extends="beans.Employee">
<key column="id"></key>
<property name="wh"></property>
</joined-subclass>

<joined-subclass name="beans.AEmployee" table="aemployee" extends="beans.Employee">
<key column="id"></key>
<property name="server"></property>
</joined-subclass>
</class>
</hibernate-mapping>```

测试.java

   public static void main(String[] args) 
    {
      Configuration cfg=new Configuration();
      cfg.configure("resources/mysql.cfg.xml");
      SessionFactory sf=cfg.buildSessionFactory();
      Session session=sf.openSession();
      Transaction t=session.beginTransaction();
      SEmployee se=new SEmployee(100,"abc","abc@gmail.com",2000,"hibernate");
      HEmployee he=new HEmployee(200,"abc","abc@gmail.com",2000,20);
      AEmployee ae=new AEmployee(300,"abc","abc@gmail.com",2000,"oracle");
      session.save(se);
      session.save(he);
      session.save(ae);
      t.commit();
      session.close();
      sf.close();
    }

异常日志:

        Sep 11, 2019 10:25:58 AM org.hibernate.Version logVersion
        INFO: HHH000412: Hibernate Core {5.4.4.Final}
        Sep 11, 2019 10:25:59 AM 

        org.hibernate.annotations.common.reflection.java.JavaReflectionManage                  
        <clinit>
        INFO: HCANN000001: Hibernate Commons Annotations {5.1.0.Final}
        Sep 11, 2019 10:26:01 AM 
        org.hibernate.engine.jdbc.connections.internal.
        DriverManagerConnectionProviderImpl configure
        WARN: HHH10001002: Using Hibernate built-in connection pool (not for 
        production use!)
        Sep 11, 2019 10:26:01 AM 
        org.hibernate.engine.jdbc.connections.internal.
        DriverManagerConnectionProviderImpl buildCreator
        INFO: HHH10001005: using driver [com.mysql.jdbc.Driver] at URL 
        [jdbc:mysql://localhost:3306/hibernatedata]
        Sep 11, 2019 10:26:01 AM 
        org.hibernate.engine.jdbc.connections.internal.
        DriverManagerConnectionProviderImpl buildCreator
        INFO: HHH10001001: Connection properties: {user=root, password=****}
        Sep 11, 2019 10:26:01 AM 
        org.hibernate.engine.jdbc.connections.internal.
        DriverManagerConnectionProviderImpl buildCreator
        INFO: HHH10001003: Autocommit mode: false
       Sep 11, 2019 10:26:01 AM 
       org.hibernate.engine.jdbc.connections.internal.
       DriverManagerConnectionProviderImpl$PooledConnections <init>
       INFO: HHH000115: Hibernate connection pool size: 10 (min=1)
       Sep 11, 2019 10:26:01 AM org.hibernate.dialect.Dialect <init>
       INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQLDialect
       Sep 11, 2019 10:26:03 AM org.hibernate.AssertionFailure <init>
       ERROR: HHH000099: an assertion failure occurred (this may indicate a 
       bug in Hibernate, but is more likely due to unsafe use of the 
       session): org.hibernate.AssertionFailure: Table hibernatedata.employee 
       not found
       Sep 11, 2019 10:26:03 AM 
       org.hibernate.engine.jdbc.connections.internal.
       DriverManagerConnectionProviderImpl$PoolState stop
      INFO: HHH10001008: Cleaning up connection pool 
      [jdbc:mysql://localhost:3306/hibernatedata]
      Exception in thread "main" org.hibernate.MappingException: Could not  
      instantiate persister 
      org.hibernate.persister.entity.JoinedSubclassEntityPersister
      at 
      org.hibernate.persister.internal.PersisterFactoryImpl.
      createEntityPersister(PersisterFactoryImpl.java:112)
      at 
      org.hibernate.persister.internal.PersisterFactoryImpl.
      createEntityPersister(PersisterFactoryImpl.java:77)
      at 
      org.hibernate.metamodel.internal.MetamodelImpl.
      initialize(MetamodelImpl.java:181)
     at org.hibernate.internal.SessionFactoryImpl.<init> 
     (SessionFactoryImpl.java:300)
     at 
     org.hibernate.boot.internal.
     SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:462)
     at 
    org.hibernate.cfg.Configuration.
    buildSessionFactory(Configuration.java:708)
    at 
    org.hibernate.cfg.Configuration.
    buildSessionFactory(Configuration.java:724)
    at test.Client_Relations.main(Client_Relations.java:17)
    Caused by: org.hibernate.AssertionFailure: Table hibernatedata.employee 
    not found
    at
    org.hibernate.persister.entity.AbstractEntityPersister.
    getTableId(AbstractEntityPersister.java:5541)
    at org.hibernate.persister.entity.JoinedSubclassEntityPersister.<init> 
    (JoinedSubclassEntityPersister.java:450)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at 
    sun.reflect.NativeConstructorAccessorImpl.newInstance
    (NativeConstructorAccessorImpl.java:62)
    at 
    sun.reflect.DelegatingConstructorAccessorImpl.
    newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at org.hibernate.persister.internal.PersisterFactoryImpl.
    createEntityPersister(PersisterFactoryImpl.java:96)
    ... 7 more

Answer 1

此错误表明数据库中不存在表Employee。

Caused by: org.hibernate.AssertionFailure: Table hibernatedata.employee 
    not found

你需要更换

    <property name="hbm2ddl.auto">update</property>

与

    <property name="hbm2ddl.auto">create</property>