延迟加载一类的 Blob 属性

发布于 2024-08-25 18:33:26 字数 2183 浏览 7 评论 0原文

我想要延迟加载 @Lob 属性。首先，我使用 javassist 来检测我的类，如下所述 http://docs.jboss.org/hibernate/core/3.3/reference/en/html/performance.html#performance-fetching-lazyproperties：代码：

我的类包含“摘要”和“标题”属性，这些属性是 Lob 和其他属性。代码：


public class News extends BaseEntity{
   .
   .
   .
   @Lob
    @Basic(fetch = FetchType.LAZY)
    public String getSummary() {
        return summary;
    }

@高球
@Basic(fetch = FetchType.LAZY)
公共字符串 getTitle() {
        返回标题；
       }

@Temporal(TemporalType.TIMESTAMP)
public Date getPublishDate() {
    return publishDate;
}


 。
   。
   。
}

首先，我从数据库加载一条新闻，并想要检索新闻的发布日期（我在下面编写我的代码）代码：


newsDAO.findByid(1L).getPublishDate();

findByid 方法是：


Code:
public News findById(Long id) throws ServiceException {
        News  entity = em.getReference(entityClass, id);
         return entity;
    }

然后，hibernate 生成这个查询：代码：


Hibernate:
    select
        news0_.id as id1_,
        news0_.entityVersion as entityVe2_1_,
        news0_.publishDate as publish15_1_,
        news0_.url as url1_
    from
        News news0_
    where
        news_.id=?

This query shows that ,it does not retrieve Lob property and fortunately lazy loading of Lob properties works well.

但是当我只加载新闻的“摘要”属性时代码：


newsDAO.findByid(1L).getSummary();

然后，hibernate 生成这些查询：代码：


Hibernate:
    select
        news0_.id as id1_,
        news0_.entityVersion as entityVe2_1_,
        news0_.publishDate as publish15_1_,
        news0_.url as url1_
    from
        News news0_
Hibernate:
    select
        news_.summary as summary1_,
        news_.title as title1_
    from
        News news_
    where
        news_.id=?

我有两个问题： 1.我只想检索“summary”属性而不是“title”属性，但hibernate查询显示它也检索“title”属性，为什么会发生这种情况？ 2.为什么hibernate会生成两个查询来仅检索新闻的摘要属性？

如果有人帮助我，我将不胜感激。科斯罗。

原文

I want to lazy load of @Lob properties.
First ,i use javassist to instrument my class as described here http://docs.jboss.org/hibernate/core/3.3/reference/en/html/performance.html#performance-fetching-lazyproperties:
Code:

My class contains "summary" and "title" properties those are Lob and other properties.
Code:


public class News extends BaseEntity{
   .
   .
   .
   @Lob
    @Basic(fetch = FetchType.LAZY)
    public String getSummary() {
        return summary;
    }

@Lob
@Basic(fetch = FetchType.LAZY)
public String getTitle() {
        return title;
       }

@Temporal(TemporalType.TIMESTAMP)
public Date getPublishDate() {
    return publishDate;
}

.

   .

   .

}


First i load one news from database and want to retrieve publishdate of news(i write my codes in below)

Code:

newsDAO.findByid(1L).getPublishDate();


and findByid method is :

Code:
public News findById(Long id) throws ServiceException {
        News  entity = em.getReference(entityClass, id);
         return entity;
    }


then ,hibernate generates this query:

Code:

Hibernate:
    select
        news0_.id as id1_,
        news0_.entityVersion as entityVe2_1_,
        news0_.publishDate as publish15_1_,
        news0_.url as url1_
    from
        News news0_
    where
        news_.id=?



This query shows that ,it does not retrieve Lob property and fortunately lazy loading of Lob properties works well.
But when i load only "summary" property of news

Code:

newsDAO.findByid(1L).getSummary();


then ,hibernate generates these queries:

Code:

Hibernate:
    select
        news0_.id as id1_,
        news0_.entityVersion as entityVe2_1_,
        news0_.publishDate as publish15_1_,
        news0_.url as url1_
    from
        News news0_
Hibernate:
    select
        news_.summary as summary1_,
        news_.title as title1_
    from
        News news_
    where
        news_.id=?


I have two qurestions:

1.I only want to retrieve "summary" property not "title" property,but hibernate query shows that it also retrieve "title" property,Why this happens?

2.Why hibernate generates two query for retrieving only summary property of news?
I would be appreciate if anyone helps me.

Khosro.