Property discriminator for many-to-many relationship

joe.ferrar · **Joined:** Thu Dec 07, 2006 3:03 am **Posts:** 1

I have a parent object that can have two different types of children (call them Red children and Blue children). My object model looks something like the following:

Code:

public class Parent {
   public long getId();
   public void setId();

   public List getRedChildren();
   public void setRedChildren(List c);

   public List getBlueChildren();
   public void setBlueChildren(List c);

   // ...
};

public class Child {
   public long getId();
   public void setId(long n);

   // ...
};

Underneath, these object model needs to map onto the following table structure:

Code:

CREATE TABLE Parent(
  id NUMBER(14) NOT NULL PRIMARY KEY,
  ... 
);

CREATE TABLE Child(
  id NUMBER(14) NOT NULL PRIMARY KEY
  ...
);

CREATE TABLE ParentChildMap(
   parent_id NUMBER(14),
   child_id NUMBER(14),
   child_type VARCHAR(1)
);

where the child_type column on ParentChildMap determines whether the child is blue or red ('B' for blue, 'R' for red). I'm trying to create a read/write mapping for this object model on to this table model. I know I can use a where clause on my many-to-many mapping for redChildren and blueChildren to only select the rows that have the appropriate child_type. But I'm trying to make this a read/write mapping, such that when I persist a parent that contains Red children, an entry is created in the ParentChildMap table with the appropriate child_type value. I've gone through the docs and the forums, but haven't found a way to achieve this. Can this be accomplished through the mapping file?

Thanks in advance.

pasha · **Joined:** Sat Nov 27, 2004 4:13 am **Posts:** 137

define two different classes (BlueChild and RedChild) which extend the Child with a discriminator column, and well everything is done.

ambro23 · **Joined:** Sat Dec 16, 2006 6:31 am **Posts:** 3

I have the same problem.

However, the proposed solution is not good, because the same child may be red or blue depending on the parent, so extending child with a discriminator column is not a good solution.

Anybody else?

batmat · **Posted:** Sat Dec 16, 2006 9:28 am

ambro23 wrote:

However, the proposed solution is not good, because the same child may be red or blue depending on the parent, so extending child with a discriminator column is not a good solution.

What do you mean? You want to change the child type at runtime, that's to say ? The delta between the good solution adviced and your requirement is not very clear.

Also Maybe open a new post to discuss your subject.

ambro23 · **Joined:** Sat Dec 16, 2006 6:31 am **Posts:** 3

batmat wrote:

Also Maybe open a new post to discuss your subject.

Ok, new topic is created. Please come to:

http://forum.hibernate.org/viewtopic.php?t=968714