Hibernate之dynamic-update，dynamic-update

Hibernate之dynamic-update，dynamic-update

問題：設置了dynamic-update, 可是事實上並沒有按照期望進行了update。

案例代碼如下：

1、持久化對象

1 package com.jdw.hibernate.entities; 2 3 import java.util.Date; 4 5 public class News { 6 private Integer id; 7 private String title; 8 private String author; 9 private Date date; 10 11 public News() { 12 // TODO Auto-generated constructor stub 13 } 14 15 public News(String title, String author, Date date) { 16 super(); 17 this.title = title; 18 this.author = author; 19 this.date = date; 20 } 21 22 @Override 23 public String toString() { 24 return "News [id=" + id + ", title=" + title + ", author=" + author 25 + ", date=" + date + "]"; 26 } 27 28 public Integer getId() { 29 return id; 30 } 31 32 public void setId(Integer id) { 33 this.id = id; 34 } 35 36 public String getTitle() { 37 return title; 38 } 39 40 public void setTitle(String title) { 41 this.title = title; 42 } 43 44 public String getAuthor() { 45 return author; 46 } 47 48 public void setAuthor(String author) { 49 this.author = author; 50 } 51 52 public Date getDate() { 53 return date; 54 } 55 56 public void setDate(Date date) { 57 this.date = date; 58 } 59 } View Code

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、測試代碼

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

		news.setAuthor("test");//注意：這裡只設置了test屬性
		news.setId(13);
		
		session.update(news);
	}

4、結果

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並沒有按照期望只update Author屬性，而是更新了所有屬性，其他屬性肯定更新成了null，壞菜了！

   網上查了資料，不少同學說要在設置dynamic-update的同時，設置select-before-update即可滿足期望，注意上面的映射文件，是設置了該屬性的。

   那問題出在哪裡？如何解決呢？

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

   先看另一段測試代碼：

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

		news.setAuthor("test");//注意：這裡只設置了test屬性
		
		session.update(news);
	}

　結果如你所願，只更新了author字段。兩項比較，dynamic-update=true,只對持久化對象起作用，對於transient臨時對象不起作用。至於為什麼這麼設計？求高人告之。