How to prevent insert complicate object to author table?

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

Hi everyone:

I want to write a BBS using Hibernate.I have two tables author and article.The accociation of author and article are 1:N. I want to implement this.When a user post a article, his name will be inserted into author table and the comment of article will be inserted into article table. When the user post topic next time his name will Not be inserted into author table again. But his article will be inserted into article table normally. The author and his article will be accociated remain. I means that I can get all the articles when I use a author's ID. I try to change the code to

Code:

<hibernate-mapping> 
   <class name="lyo.hotmail.htest.Parent"> 
      <id name="id" type="int" unsaved-value="0"> 
        <generator class="identity"/> 
     </id> 
     <property name="name" unique="true"/> 
     <set name="children" lazy="true" inverse="true" cascade="all"> 
        <key  column="parent_id"/> 
       <one-to-many class="lyo.hotmail.htest.Child"/> 
     </set> 
   </class> 
   <class name="lyo.hotmail.htest.Child"> 
      <id name="id" type="int" unsaved-value="any"> 
        <generator class="identity"/> 
     </id> 
     <property name="name"/> 
     <many-to-one  name="parent" column="parent_id" not-null="true"/> 
   </class> 
</hibernate-mapping> 

But when the author post the second article his name will be inserted into author table again! The author name can't complicate in author table.
How to fix this?

Thks in advanced!

michael · **Posted:** Sat Dec 20, 2003 8:02 pm

Simple: Load the Author first from the DB, if it does not allready exist create a new one and save it. Then add the Article to the collection.

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

gloeglm wrote:

Simple: Load the Author first from the DB, if it does not allready exist create a new one and save it. Then add the Article to the collection.

Thks for your reply.

You means I must code myself to fix it?

It is that:

Code:

String authorname=request.getParameter("authorname");
Auhor au=null;
Author au=session.find("from Author au where au.name=?",authorname,Hibernate.STRING);
if(au.isEmpty()){
   au=new Author();
   au.setName(authorname);
   Article art=new Article();
   art.setComment(...);
   au.addArticle(art);
   session.save(au);
}else{
   au.addArticle(art);
   session.save(au);
}

You mean I must do this every time? Is there more easy method to do this.For example, Can I do this in xml ?

michael · **Posted:** Sat Dec 20, 2003 8:31 pm

Yes you have to. But use session.update() if the Author allready exists. Or use session.saveOrUpdate()

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

gloeglm wrote:

Yes you have to. But use session.update() if the Author allready exists. Or use session.saveOrUpdate()

It seems I have to do this. :(

I change the code to:

Code:

String authorname=request.getParameter("authorname"); 
Auhor au=null; 
Author au=session.find("from Author au where au.name=?",authorname,Hibernate.STRING); 
if(au.isEmpty()){ 
   au=new Author(); 
   au.setName(authorname); 
   Article art=new Article(); 
   art.setComment(...); 
   au.addArticle(art); 
   session.save(au); 
}else{ 
   au.addArticle(art); 
   session.update(au);   // or use session.saveOrUpdate(au);
}

michael · **Posted:** Sat Dec 20, 2003 8:40 pm

This obviously wont work, session.find() returns a collection, no Author object. But I'm sure you will figure this out yourself :)

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

Thks

Would you tell me when I must use proxy in hibernate? I had been puzzled all the time after I saw the example in hibernate documents.

It use a proxy in hiber.hbm.xml. I really don't know what to do with that? How to use "proxy"?

michael · **Posted:** Sat Dec 20, 2003 8:43 pm

If you use a proxy for a class, hibernate won't load the class completely upon load (for example when it is used as a property of another object), but rather lazily when it is first acessed.

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

gloeglm wrote:

If you use a proxy for a class, hibernate won't load the class completely upon load (for example when it is used as a property of another object), but rather lazily when it is first acessed.

You mean proxy can lazy the object? But I can lazy the object using "lazy=true" in XX.hbm.xml <set .... . ></set>

Another mean is if a class have a property of another class.will it use proxy? I don't know how to use it exactly. :(

michael · **Posted:** Sat Dec 20, 2003 8:56 pm

Quote:

You mean proxy can lazy the object? But I can lazy the object using "lazy=true" in XX.hbm.xml <set .... . ></set>

No, you can lazy load a collection. To lazy load a class, you need a proxy.

Quote:

Another mean is if a class have a property of another class.will it use proxy?

Yes

Quote:

I don't know how to use it exactly. :(

Then just try it.[/quote]

michael · **Posted:** Sat Dec 20, 2003 8:58 pm

And read http://www.hibernate.org/hib_docs/reference/html/performance.html#performance-s4

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

Thks in advanced !

I will read it carefully :)