one class - one table - how?

sven · **Posted:** Wed Dec 10, 2003 3:42 pm

I have one class MyDirectory.java which is supposed to represent something like a usual directory.
Every directory might have several subdirectories.

I have one database table directories.

I'd like to create some objects of MyDirectory with one parent directory and a structure below, e.g.:

Code:

-parentDir
   -childDir1
   -childDir2
   -childDir3

Finally I'd like to save all of them by using:
session.save(parentDir);

How is this possible (which mapping?)?
Is it possible without having to tell each childDir its parent?

Thanks a lot for your help!

Here is some code:

MyDirectory.java

Code:

package test;

import java.util.HashSet;
import java.util.Set;

public class MyDirectory {

    private Long id;
    private String name;
    private Set subDirs = new HashSet();

    public MyDirectory() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set getSubDirs() {
        return subDirs;
    }

    public void setSubDirs(Set subDirs) {
        this.subDirs = subDirs;
    }
}

TestMyDirectory.java

Code:

[...]
MyDirectory parent = new MyDirectory();
parent.setName("AAA");

//create child directories
MyDirectory child1 = new MyDirectory();
child1.setName("BBB");
MyDirectory child2 = new MyDirectory();
child2.setName("CCC");
MyDirectory child3 = new MyDirectory();
child3.setName("DDD");

//add children to parent list
parent.getSubDirs().add(child1);
parent.getSubDirs().add(child2);
parent.getSubDirs().add(child3);

// save parent directory
session.save(parent);
session.flush();
[...]

MyDirectory.hbm.xml

Code:

<?xml version="1.0"?>

<!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.MyDirectory"
        table="directories"
    >

        <id
            name="id"
            column="id"
            type="long"
        >
            <generator class="native"/>
        </id>

        <property
            name="name"
            type="string"
            column="name"
        />

        <set
            name="subDirs"
            table="directories"
            lazy="false"
            inverse="false"
            cascade="all"
            sort="unsorted"
        >

              <key
                  column="parent"
              />

              <one-to-many
                  class="test.MyDirectory"
              />
        </set>

    </class>
</hibernate-mapping>

Database

Code:

CREATE TABLE directories (
  id bigint(20) NOT NULL auto_increment,
  name varchar(255) NOT NULL default '',
  parent bigint(20) default '0',
  PRIMARY KEY  (id)
) TYPE=InnoDB;

emmanuel · **Posted:** Wed Dec 10, 2003 5:51 pm

sven wrote:

How is this possible (which mapping?)?

Just the one you post

sven wrote:

Is it possible without having to tell each childDir its parent?

Yes, this is the purpose of inverse="false" in your set.

beware the default value in parent bigint(20) default '0'
It works because you don't bi-direct your association.

I must have missed something, because you're the first guy who post a question and the appropriate answer the same time ;-)

sven · **Posted:** Thu Dec 11, 2003 3:48 am

Some kind of "Configuration().add()" and ClassLoader-error occurs with these files. Sorry, I don't have the exact error message here. I'll post it later.

When I leave the part with the set out of the mapping it works (of course not the way I'd like it to work, but no error occurs).

That's why I think that something has to be wrong with the set...

emmanuel · **Posted:** Thu Dec 11, 2003 7:28 am

Copy/pastle the exact mapping and POJO for my first post and it worked with hibernate 2.1rc1 and HSQLDB (I let schema export doing the DDL)

sven · **Posted:** Thu Dec 11, 2003 1:47 pm

Unbelievable, it works (using Hibernate 2.1rc1 and MySQL 4)!

Don't really know what went wrong, but thanks a lot for your help though! :)