Is this the right way for cascade CRUD operations?

Lasek · **Joined:** Fri Apr 29, 2005 10:57 pm **Posts:** 41

Hibernate version: 3.0

Yes I do own Hibernate in Action and it does not really answer this question...

I have the following relationship between two objects: a Client and a Project. A client can have as many projects as he wants (one-to-many) and a project can have only one client as a parent (many-to-one).

Here are the .hbm.xml files:

Client:

Code:

...
    <class name="Client" table="clients">
    
       <cache usage="read-write"/>
    
        <id name="ID" column="ID" type="java.lang.Long">
            <generator class="native"/>
        </id>        
...
        
        <set name="projects" table="projects" lazy="true" cascade="all">
           <cache usage="read-write"/>
           <key column="clientID"/>
           <one-to-many class="org.ablogic.projects.Project"/>
        </set>

...

Here's Project:

Code:

...

    <class name="Project" table="projects">
    
       <cache usage="read-write"/>
    
        <id name="ID" column="ID" type="java.lang.Long">
            <generator class="native"/>
        </id>
        
        <many-to-one name="client" class="org.ablogic.clients.Client" column="clientID" cascade="save-update" />

...

First question: are the "cascade" relationships correct? If my client is deleted, I want all the projects to be deleted as well - therefore it's "all".

If a project is deleted - I don't want to delete the client, but I still want to keep save/update going (even though it doesn't seem to work - I still have to delete objects manually).

So am I on the right track here?

Ok, now here's the CRUD actions in my struts action file:

Code:

public class ProjectCRUDAction extends DispatchAction
{
   public ActionForward create( ActionMapping mapping, ActionForm aform, HttpServletRequest request,
         HttpServletResponse response )
   {
      ProjectForm form = (ProjectForm)aform;
      Project project = new Project();
      form.copyTo(project);
      
      HibernateUtil.beginTransaction();
      HibernateUtil.getSession().save(project);
      project.getClient().getProjects().add(project);
      HibernateUtil.getSession().update(project.getClient());
      HibernateUtil.commitTransaction();
      

      request.setAttribute("project",project);
      
      return mapping.findForward("success");
   }
   
   public ActionForward edit( ActionMapping mapping, ActionForm aform, HttpServletRequest request,
         HttpServletResponse response )
   {
      ProjectForm form = (ProjectForm)aform;
      Project project = form.getProject();
      
      if (! project.getClient().equals(form.getClient()) )
         project.getClient().getProjects().remove(project);
      
      form.copyTo(project);
      project.getClient().getProjects().add(project);
      
      HibernateUtil.beginTransaction();
      HibernateUtil.getSession().update(project);
      HibernateUtil.getSession().update(project.getClient());
      HibernateUtil.commitTransaction();

      request.setAttribute("project",project);
      
      return mapping.findForward("success");
   }
   
   public ActionForward delete( ActionMapping mapping, ActionForm aform, HttpServletRequest request,
         HttpServletResponse response )
   {
      ProjectForm form = (ProjectForm)aform;
      Project project = form.getProject();
      project.getClient().getProjects().remove(project);
      
      HibernateUtil.beginTransaction();
      HibernateUtil.getSession().delete(project);
      HibernateUtil.getSession().update(project.getClient());
      HibernateUtil.commitTransaction();
      
      request.setAttribute("project",project);
      
      return mapping.findForward("success");
   }
}

So that's pretty muc creating/editing/deleting (according to the method name).

It seems that I'm doing an awful lot of extra work here - such as removing the project from the old client, and adding it to new client, and setting all those bi-directional references...

Well my question is - am I doing all the neccessary work, or is some of it redundant?

Thanks for your replies!

Lasek · **Joined:** Fri Apr 29, 2005 10:57 pm **Posts:** 41

Hmm is there no support here?

I did buy the book and it doesn't answer a basic question like this, if this is not a place to get support, can somebody point me to it?

fdelisle · **Posted:** Tue Jun 28, 2005 8:26 am

Ok, well, I see many problems with your mappings.

First, you should know about the inverse attribute for collections. Read on it. Second, you should read about Parent/Child relations, you would notice you need to use "all-delete-orphans" not simply "all"
Third, your code Client.addProject( Project project ) should look like this:

Code:

    project.setClient( this );
    projects.add( project );

This is definitevely covered in the book. There is a section for that specific use case right in the online doc.

Lasek · **Joined:** Fri Apr 29, 2005 10:57 pm **Posts:** 41

Quote:

Ok, well, I see many problems with your mappings.

Be so nice and point them out? :)

Quote:

First, you should know about the inverse attribute for collections. Read on it.

I know what inverse does, it prevents Hibernate from updating the same table twice when you have bi-directional collections... In my case the collection isn't really bi-directional, since a client can have many projects (one-to-many) but a project can have only one client (many-to-one), and I can't use "inverse" in many-to-one associations.

Quote:

Second, you should read about Parent/Child relations, you would notice you need to use "all-delete-orphans" not simply "all"

I have read that stuff, and my understanding is when I use all-delete-orphan it would delete projects that don't have any clients... But if I specify "all", wouldn't that automatically delete project when a client is deleted?

Quote:

Third, your code Client.addProject( Project project ) should look like this:

project.setClient( this );
projects.add( project );

Well that's the same as what I do (except I don't do it inside my client):

Code:

...
form.copyTo(project);  // this does project.setClient( client )
...
project.getClient().getProjects().add(project);  // and this is the bi-direction
...

Quote:

This is definitevely covered in the book. There is a section for that specific use case right in the online doc.

Could you point to what I should read up on? So far everything works just fine, I just wanted to know if I have excessive code... According to your post I'm doing everything right, except our disagreement on the cascading options...