报错：org.hibernate.AssertionFailure: null id in com.tt.hibernate.entities.News entry (don't flush the Session after an exception occurs)

在使用hibernate创建数据库的表格时，出现了如下报错：

十二月 28, 2016 10:17:02 上午 org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: HHH000389: Unsuccessful: create table NEWS (ID integer not null auto_increment, TITLE varchar(255), AUTHOR varchar(255), DATE datetime, DESC varchar(255), CONTENT varchar(255), IMAGE longblob, primary key (ID)) ENGINE=InnoDB
十二月 28, 2016 10:17:02 上午 org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DESC varchar(255),
CONTENT varchar(255),
IMAGE longblob,
' at line 6
十二月 28, 2016 10:17:02 上午 org.hibernate.tool.hbm2ddl.SchemaExport execute
INFO: HHH000230: Schema export complete
Hibernate: 
create table NEWS (
ID integer not null auto_increment,
TITLE varchar(255),
AUTHOR varchar(255),
DATE datetime,
DESC varchar(255),
CONTENT varchar(255),
IMAGE longblob,
primary key (ID)
) ENGINE=InnoDB
Hibernate: 
insert 
into
NEWS
(TITLE, AUTHOR, DATE, DESC, CONTENT, IMAGE) 
values
(?, ?, ?, ?, ?, ?)
十二月 28, 2016 10:17:03 上午 org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
WARN: SQL Error: 1064, SQLState: 42000
十二月 28, 2016 10:17:03 上午 org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DESC, CONTENT, IMAGE) values ('CC', 'cc', '2016-12-28 10:17:02.785', 'DESC', 'CO' at line 1
destroy...
十二月 28, 2016 10:17:03 上午 org.hibernate.AssertionFailure <init>
ERROR: HHH000099: an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session): org.hibernate.AssertionFailure: null id in com.tt.hibernate.entities.News entry (don't flush the Session after an exception occurs)

各部分代码如下：

HibernateTest.java：

package com.tt.hibernate.entities;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Date;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.jdbc.Work;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class HibernateTest {

    private SessionFactory sessionFactory;
    private Session session;
    private Transaction transaction;
    
    @Before
    public void init(){
        System.out.println("init...");
        
        Configuration configuration = new Configuration().configure();
        ServiceRegistry serviceRegistry = 
                new ServiceRegistryBuilder().applySettings(configuration.getProperties())
                                            .buildServiceRegistry();
        sessionFactory = configuration.buildSessionFactory(serviceRegistry);
        
        session = sessionFactory.openSession();
        
        transaction = session.beginTransaction();
    }
    
    @After
    public void destroy() {
        System.out.println("destroy...");
        
        transaction.commit();
        session.close();
        sessionFactory.close();
    }
    
    @Test
    public void testBlob() throws IOException, SQLException{
        News news = new News();
        
        news.setAuthor("cc");
        news.setTitle("CC");
        news.setDesc("DESC");
        news.setContent("CONTENT");
        news.setDate(new Date());
        
        InputStream stream = new FileInputStream("SHQ.jpg");
        Blob image = Hibernate.getLobCreator(session)
                              .createBlob(stream, stream.available());
        
        news.setImage(image);
        
        session.save(news);
    }

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>
    
        <!-- Hibernate连接数据库的基本信息 -->
        <property name="conncection.username">root</property>
        <property name="connection.password">1234</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/Hibernate</property>
        
        <!-- Hibernate的基本配置 -->
        
        <!-- Hibernate使用的数据库方言 -->
        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
        
        <!-- 运行时是否打印SQL -->
        <property name="show_sql">true</property>
        
        <!-- 运行时是否格式化SQL -->
        <property name="format_sql">true</property>
        
        <!-- 生成数据表的策略 -->
        <property name="hbm2ddl.auto">create</property>
        
        <!-- 设置Hibernate的事务隔离级别 ：2代表读已提交-->
        <property name="connection.isolation">2</property>
        
        <!-- 删除对象后，使其OID设置为null -->
        <property name="use_identifier_rollback">true</property>      
        
        <!-- 配置C3P0数据源 -->
        <property name="hibernate.c3p0.max_size">10</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="hibernate.c3p0.acquire_increment">2</property>
        
        <property name="hibernate.c3p0.idle_test_period">2000</property>
        <property name="hibernate.c3p0.timeout">2000</property>
        
        <property name="hibernate.c3p0.max_statements">10</property>
        
        <!-- 设定JDBC的statement读取数据的时候每次从数据库中取出的记录条数 -->
        <property name="hibernate.jdbc.fetch_size">100</property>
        
        <!-- 设定对数据库进行批量删除，批量更新和批量插入的时候的批次大小 -->
        <property name="jdbc.batch_size">30</property>
         
        <!-- 需要关联的hibernate映射文件 .jbm.xml -->
        <mapping resource="com/tt/hibernate/entities/News.hbm.xml"/>
        <!--  <mapping resource="com/tt/hibernate/entities/Worker.hbm.xml"/>-->
        
    </session-factory>
</hibernate-configuration>

News.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2016-12-25 12:12:49 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping package="com.tt.hibernate.entities">
    <class name="News" table="NEWS">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="title" type="java.lang.String">
            <column name="TITLE" />
        </property>
        <property name="author" type="java.lang.String">
            <column name="AUTHOR" />
        </property>
        <property name="date" type="java.util.Date">
            <column name="DATE" />
        </property>
        <property name="desc" type="java.lang.String">
            <column name="DESC" />
        </property>
        <property name="content" type="java.lang.String">
            <column name="CONTENT" />
        </property>
        <property name="image" type="java.sql.Blob">
            <column name="IMAGE" />
        </property>
    </class>
</hibernate-mapping>

根据报错信息，定位到SQL语句的第6行：Content varchar(255)

 症状分析：

如果将News.hbm.xml文件里的desc属性设置改为下面的映射派生属性，运行正常而且可以看到news表格里是没有DESC这一列。

那么为什么会出现这样的现象？为什么desc只能作为派生属性存在呢？它和title、author和date存在什么区别？唯一的区别 后三者作为参数参与了new News对象的创建。具体原因还需要深究。