Hibernate: 根据实体类自动创建/更新数据库表

我有以下实体类(在 Groovy 中) :

import javax.persistence.Entity
import javax.persistence.Id
import javax.persistence.GeneratedValue
import javax.persistence.GenerationType


@Entity
public class ServerNode {


@Id
@GeneratedValue(strategy = GenerationType.AUTO)
Long id


String firstName
String lastName


}

以及我的  寄存器.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0">
<persistence-unit name="NewPersistenceUnit">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/Icarus"/>
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
<property name="hibernate.connection.username" value="root"/>
<property name="hibernate.connection.password" value=""/>
<property name="hibernate.archive.autodetection" value="class"/>
<property name="hibernate.show_sql" value="true"/>
<property name="hibernate.format_sql" value="true"/>
<property name="hbm2ddl.auto" value="create"/>
</properties>
<class>net.interaxia.icarus.data.models.ServerNode</class>
</persistence-unit>
</persistence>

还有剧本:

import javax.persistence.EntityManager
import javax.persistence.EntityManagerFactory
import javax.persistence.Persistence
import net.interaxia.icarus.data.models.ServerNode


def factory = Persistence.createEntityManagerFactory("NewPersistenceUnit")
def manager = factory.createEntityManager()


manager.getTransaction().begin()


manager.persist new ServerNode(firstName: "Test", lastName: "Server")


manager.getTransaction().commit()

数据库 伊卡洛斯存在，但目前没有表。我希望 Hibernate 根据实体类自动创建和/或更新表。我要怎么做？

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小开

You might try changing this line in your persistence.xml from

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

to:

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

This is supposed to maintain the schema to follow any changes you make to the Model each time you run the app.

Got this from JavaRanch

小开
最佳答案

I don't know if leaving hibernate off the front makes a difference.

The reference suggests it should be hibernate.hbm2ddl.auto

A value of create will create your tables at sessionFactory creation, and leave them intact.

A value of create-drop will create your tables, and then drop them when you close the sessionFactory.

Perhaps you should set the javax.persistence.Table annotation explicitly?

Hope this helps.

小开

Sometimes depending on how the configuration is set, the long form and the short form of the property tag can also make the difference.

e.g. if you have it like:

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

try changing it to:

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

There is one very important detail, than can possibly stop your hibernate from generating tables (assuming You already have set the hibernate.hbm2ddl.auto). You will also need the @Table annotation! 

@Entity
@Table(name = "test_entity")
public class TestEntity {
}

It has already helped in my case at least 3 times - still cannot remember it ;)

PS. Read the hibernate docs - in most cases You will probably not want to set hibernate.hbm2ddl.auto to create-drop, because it deletes Your tables after stopping the app.

小开

In applicationContext.xml file:

<bean id="entityManagerFactoryBean" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="dataSource" ref="dataSource" />
<!-- This makes /META-INF/persistence.xml is no longer necessary -->
<property name="packagesToScan" value="com.howtodoinjava.demo.model" />
<!-- JpaVendorAdapter implementation for Hibernate EntityManager.
Exposes Hibernate's persistence provider and EntityManager extension interface -->
<property name="jpaVendorAdapter">
<bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />
</property>
<property name="jpaProperties">
<props>
<prop key="hibernate.hbm2ddl.auto">update</prop>
<prop key="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</prop>
</props>
</property>
</bean>
小开

In my case table was not created for the first time without last property listed below:

<properties>
<property name="hibernate.archive.autodetection" value="class"/>
<property name="hibernate.show_sql" value="true"/>
<property name="hibernate.format_sql" value="true"/>
<property name="hbm2ddl.auto" value="create-drop"/>
<!-- without below table was not created -->
<property name="javax.persistence.schema-generation.database.action" value="drop-and-create" />
</properties>

used Wildfly's in-memory H2 database

小开

In support to @thorinkor's answer I would extend my answer to use not only @Table (name = "table_name") annotation for entity, but also every child variable of entity class should be annotated with @Column(name = "col_name"). This results into seamless updation to the table on the go.

For those who are looking for a Java class based hibernate config, the rule applies in java based configurations also(NewHibernateUtil). Hope it helps someone else.

小开
  1. TO CREATING TABLE AUTOMATIC , NO CONNECTION WITH ANNOTATIONS
  2. FOR THAT WE NEED TO CHANGE "hibernate.cfg.xml" as like.
 <property name="hbm2ddl.auto">update</property>

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