Hibernate之dynamic-update

问题：设置了dynamic-update, 可是事实上并没有按照期望进行了update。

案例代码如下：

1、持久化对象

package com.jdw.hibernate.entities;

import java.util.Date;

public class News {
    private Integer id;
    private String title;
    private String author;
    private Date date;

    public News() {
        // TODO Auto-generated constructor stub
    }

    public News(String title, String author, Date date) {
        super();
        this.title = title;
        this.author = author;
        this.date = date;
    }

    @Override
    public String toString() {
        return "News [id=" + id + ", title=" + title + ", author=" + author
                + ", date=" + date + "]";
    }

    public Integer getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }
}

2、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 2016-3-8 20:08:39 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
	<class name="com.jdw.hibernate.entities.News" table="NEWS" lazy="false" select-before-update="true" dynamic-update="true">
		<id name="id" type="java.lang.Integer" unsaved-value="110">
			<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>
	</class>
</hibernate-mapping>

3、测试代码

	@Test
	public void testDynamicUpdate() {
		News news =new News();

		news.setAuthor("test");//注意：这里只设置了test属性
		news.setId(13);
		
		session.update(news);
	}

4、结果

Hibernate: 
    select
        news_.ID,
        news_.TITLE as TITLE2_1_,
        news_.AUTHOR as AUTHOR3_1_,
        news_.DATE as DATE4_1_ 
    from
        NEWS news_ 
    where
        news_.ID=?
Hibernate: 
    update
        NEWS 
    set
        TITLE=?,
        AUTHOR=?,
        DATE=? 
    where
        ID=?

   hibernate并没有按照期望只update Author属性，而是更新了所有属性，其他属性肯定更新成了null，坏菜了！

   网上查了资料，不少同学说要在设置dynamic-update的同时，设置select-before-update即可满足期望，注意上面的映射文件，是设置了该属性的。

   那问题出在哪里？如何解决呢？

   --------------------------------------------------------------------------------

   先看另一段测试代码：

        @Test
	public void testDynamicUpdate2() {
		News news =(News) session.get(News.class, 13);

		news.setAuthor("test");//注意：这里只设置了test属性
		
		session.update(news);
	}

　结果如你所愿，只更新了author字段。两项比较，dynamic-update=true,只对持久化对象起作用，对于transient临时对象不起作用。至于为什么这么设计？求高人告之。