Sun, 12 Jun 2005 14:44:00 GMT

问题提出�Q?/STRONG>最�q�项目出��C��个Article持久�c�，该持久类拥有一个Clob属性用于记录文章的内容!�C�Z��如下:

public class Article implements Serializable{
    public Long articleId;
    public String author;
    public String title;
    public Date created;
    public Clob content;

//getter
//setter
}

后来发现�Q�在查找文章列表的时候，每个Article都要从数据库中加载出content�Q�严重媄(ji��ng)响效率！

解决�Ҏ(gu��)��1�Q?/FONT>

在网上找相关的资料，利用hql可以解决问题:

select new Article(a.articleId,a.author,a.title,a.created) from Article as a where

记得要�ؓ(f��) Article ��d��构造函敎ͼ�像上面的hql需要构造函数如:

public Article(Long articleId,String author,String title,Date create){
this.articleId = articleId;
this.author = author;
this.title =  title;
this.create = create;
}

解决�Ҏ(gu��)��2�Q?/FONT>

然而这样子做，列表里面的Article�q��(sh��)��够轻量，于是�H�然有天在Hibernate官方�|�站扑և�更好的解��x(ch��ng)��法！那就是所谓的Light Weight模式�Q�示例代码如下：(x��)

public class ArticleInfo implements Serializable{
    public Long articleId;
    public String author;
    public String title;
    public Date created;

//getter
//setter
}

public class Article extends ArticleInfo{
    public Clob content;

//getter
//setter
}

xml version="1.0" encoding="UTF-8"?>
DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping>
<class name="test.ArticleInfo" table="test_article" polymorphism="explicit" >
<id name="articleId" column="article_id" type="java.lang.Long" length="30">
<generator class="sequence">
<param name="sequence">article_seqparam>
generator>
id>
<property name="authorId" column="author_id" type="java.lang.String" length="10" not-null="true"/>

<property name="title" column="title" type="java.lang.String" length="10" not-null="true"/>

<property name="created" column="created" type="java.util.Date" not-null="true"/>
class>
hibernate-mapping>

xml version="1.0" encoding="UTF-8"?>
DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping>
<class name="test.Article" table="test_article" polymorphism="explicit" >
<id name="articleId" column="article_id" type="java.lang.Long" length="30">
<generator class="sequence">
<param name="sequence">article_seqparam>
generator>
id>
<property name="authorId" column="author_id" type="java.lang.String" length="10" not-null="true"/>

<property name="title" column="title" type="java.lang.String" length="10" not-null="true"/>

<property name="created" column="created" type="java.util.Date" not-null="true"/>

<property name="content" column="content" type="java.sql.Clob" not-null="true"/>
class>
hibernate-mapping>

记得要加�?polymorphism="explicit" 表示为多�?

�q�样子，当我们需要加载大对象content的时候可�?BR>
session.load(Article.class,articleId);
OR
String hql="select a from Article as a where...";

如果�Q�不需要用到大对象�Q�则可以

session.load(ArticleInfo.class,articleId);
OR
String hql="select a from ArticleInfo as a where ...";

一�?/a> 2005-06-12 22:44 发表评论

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