Question

这是一些实体：

@Entity
public class Forest {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;


    public Forest() {
    }

    public long getId() {
        return id;
    }

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

我想在表林中插入一些元素：

public class Main {
private static EntityManagerFactory emf = 
       Persistence.createEntityManagerFactory("server");

    public static void main(String[] args) {

        EntityManager em = emf.createEntityManager();
        EntityTransaction trx = em.getTransaction();
        Forest forest = new Forest();


        trx.begin();
        em.persist(forest);
        trx.commit();

    }
}

抛出异常：

Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.exception.SQLGrammarException: Table 'server.forest' doesn't exist

Caused by: org.hibernate.exception.SQLGrammarException: Table 'server.forest' doesn't exist

我的persistence.xml文件包含设置：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
   <persistence-unit name="server">
      <provider>org.hibernate.ejb.HibernatePersistence</provider>

      <properties>
          <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
          <property name="javax.persistence.jdbc.url"               value="jdbc:mysql://localhost:3306/server"/>
          <property name="javax.persistence.jdbc.user" value="root" />
          <property name="javax.persistence.jdbc.password" value="root" />
          <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
          <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
      </properties>
   </persistence-unit>
</persistence>

当我删除@GeneratedValue（strategy = GenerationType.AUTO）并为forest设置id时： forest.setID（1），没有异常并且已生成表。所以，id的自动生成不起作用，我不知道为什么。

Answer 1

根据配置，org.hibernate.dialect.HSQLDialect与MySQL数据库一起使用。使用MySQL方言而不是HSQL之一可能会有所帮助。使用了可能的InnoDB - 如果是这样的话，那么MySQL5InnoDBDialect就可以了。

JPA不从实体生成表

1 个答案: