Question

也许这是在stackoverflow上有明确答案的常见问题。但经过2个小时的搜索，我找不到答案。

我是hibernate的新手并使用maven。我正在使用this tutorial作为注释基础，并进行了一些更改。但是，它不起作用。我使用了一些xml映射文件。我甚至添加了用于hibernate xml-base的 Employee.hbm.xml 。

在此行＆gt;＆gt; session.persist（e1）; 它会抛出异常

Employee.java

import javax.persistence.*;
import javax.persistence.Entity;

@Entity
@Table(name = "employee")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="type",discriminatorType=DiscriminatorType.STRING)
@DiscriminatorValue(value="employee")

public class Employee {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)

    @Column(name = "id")
    private int id;

    @Column(name = "name")
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

Main.java

import org.hibernate.*;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;


public class Main {
    public static void main(String[] args) {
        Configuration configuration = new Configuration();
        configuration.configure("hibernate.cfg.xml");
        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(
                configuration.getProperties()).build();

        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(serviceRegistry);
        Session session = sessionFactory.openSession();

        Transaction t = session.beginTransaction();

        Employee e1 = new Employee();
        e1.setName("sonoo");

        Regular_Employee e2 = new Regular_Employee();
        e2.setName("Vivek Kumar");
        e2.setSalary(50000);
        e2.setBonus(5);

        Contract_Employee e3 = new Contract_Employee();
        e3.setName("Arjun Kumar");
        e3.setPay_per_hour(1000);
        e3.setContract_duration("15 hours");

        session.persist(e1);
        session.persist(e2);
        session.persist(e3);

        t.commit();
        session.close();
        System.out.println("success");
    }
}

Employee.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="Employee" table="employee" discriminator-value="employee">
        <id name="id">
            <generator class="increment"></generator>
        </id>

        <discriminator column="type" type="string"></discriminator>
        <property name="name"></property>

        <subclass name="Regular_Employee" discriminator-value="reg_emp">
            <property name="salary"></property>
            <property name="bonus"></property>
        </subclass>

        <subclass name="Contract_Employee" discriminator-value="con_emp">
            <property name="pay_per_hour"></property>
            <property name="contract_duration"></property>
        </subclass>

    </class>

</hibernate-mapping>

hibernate.cfg.xml中

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

    <session-factory>
        <property name="hbm2ddl.auto">update</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
        <property name="connection.username">root</property>
        <property name="connection.password">123</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <mapping resource="Employee.hbm.xml"/>
        <mapping class="Employee"/>
        <mapping class="Contract_Employee"/>
        <mapping class="Regular_Employee"/>
    </session-factory>

</hibernate-configuration>

例外文字

Exception in thread "main" org.hibernate.MappingException: Unknown entity: Employee
    at org.hibernate.internal.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:781)
    at org.hibernate.internal.SessionImpl.getEntityPersister(SessionImpl.java:1529)
    at org.hibernate.engine.internal.ForeignKeys.isTransient(ForeignKeys.java:225)
    at org.hibernate.event.internal.AbstractSaveEventListener.getEntityState(AbstractSaveEventListener.java:510)
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:99)
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:58)
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:775)
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:748)
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:753)
    at Main.main(Main.java:36)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

Answer 1

这个问题

Configuration configuration = new Configuration();
configuration.configure("hibernate.cfg.xml");
ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(
                    configuration.getProperties()).build();

SessionFactory sessionFactory = new Configuration().configure()
   .buildSessionFactory(serviceRegistry);

您尝试两次配置。这不是必要的

Configuration configuration = new Configuration();
        configuration.configure("hibernate.cfg.xml");

您无法使用这种方式配置Hibernate 5.只需为配置执行此操作

SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();

How to configure Hibernate 5

org.hibernate.MappingException：未知实体Employee

1 个答案: