关于hibernate中提示can not create table ******

最近这两天,一直在搞hibernate,被 其中一个问题困扰了好久.在网上找了好久,一直都没有找到可行的方法,把jdk,jre,tomcat,装了拆,拆了装,可就是搞不好.实在是没有办法,又重新建了一个项目来测试,,从一点一滴开始试.所有的代码全部都手写,,,,可是问题依旧还在.

之所以一直没有找到解决办法,其实是自己的思维一直局限在一处,,,一直在想着hibernate只要把配置文件配置好,它就可以自己在数据库创建表结构,自己增删改查,相当的方便,可是自己 当时成功了,为什么这次却一而再再而三的失败呢....后来再想,要不创建一个数据库,然后再创建一个表.直接用hibernate插入数据试试....没想到竟然没有报错,当时那个心情啊....

现将错误代码贴上:

WARN: Table 'myapp.user' doesn't exist
Exception in thread "main" org.hibernate.exception.SQLGrammarException: could not extract ResultSet
	at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:80)
	at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
	at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:126)
	at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:112)
	at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:91)
	at org.hibernate.id.IncrementGenerator.initializePreviousValueHolder(IncrementGenerator.java:132)
	at org.hibernate.id.IncrementGenerator.generate(IncrementGenerator.java:69)
	at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:118)
	at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:209)
	at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:55)
	at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:194)
	at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:49)
	at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
	at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:715)
	at org.hibernate.internal.SessionImpl.save(SessionImpl.java:707)
	at org.hibernate.internal.SessionImpl.save(SessionImpl.java:702)
	at com.huangchao.model.HibernateTest.main(HibernateTest.java:21)

　　上面显示的错误提示是不能执行结果集,,,,,,,原因就是没有创建表,那当然就不能执行了.

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'myapp.user' doesn't exist
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at com.mysql.jdbc.Util.getInstance(Util.java:387)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:939)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3878)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3814)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2478)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2625)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2551)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1861)
    at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1962)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:82)
    ... 12 more

看到没有,这上面显示的就是表不存在....

经检查.....hibernate.cfg.xml中有一个配置是这样写的:

<property name="hibernate.hbm2dll">create</property>

一看,不对呀,如果要想自动建表的话那应该是这样的啊:

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

原来是自己少打了.auto啊,千万要注意,.auto是不能少的,重要的事说三遍:

.auto是不能少

.auto是不能少

.auto是不能少

最后得出的结论是:

hibernate在没有手动为数据库创建特定的表的时候,且在配置文件里没有设置自动创建表,,这时就会报错.

完整代码如下:

Model:User.java

package com.huangchao.model;

public class User {

    private int id ;
    private String username ;
    private String password ;
    
    public User(){
        
    }
    public User(String username,String password){
        this.username = username;
        this.password = password;
        
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    
    
}

Mapping:User.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="com.huangchao.model.User" table="user">
<id name="id" type="int">
    <column name="id"></column>
    <generator class="increment"></generator>
</id>
<property name="username"  type="java.lang.String">
    <column name="username" />
</property>
<property name="password"  type="java.lang.String">
    <column name="password" />
</property>
</class>
</hibernate-mapping>

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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>
  <!-- 设置数据库的基本连接信息 -->
  <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
  
  <property name="hibernate.connection.url">jdbc:mysql:///myapp?characterEncoding=utf8</property>
  <property name="hibernate.connection.username">root</property>
  <property name="hibernate.connection.password">root</property>
  <!-- 设定数据库言 -->
  <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
  <!-- 设置数据 库的SQL语句的格式-->
      <property name="hibernate.show_sql">true</property>
      <property name="hibernate.format_sql">true</property>
      <property name="hibernate.hbm2ddl">create</property>
      <mapping resource="com/huangchao/model/User.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

Test:HibernateTest.java

package com.huangchao.model;


import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

public class HibernateTest {


    public static void main(String[] args) {
        Configuration config = new Configuration().configure();
        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(config.getProperties()).build();
        SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
        Session session = sessionFactory.openSession();
        
        User user = new User("zhoubin","33333");
        session.save(user);
        Transaction tx = session.beginTransaction();
        tx.commit();
        session.close();
    }

}