[1]Hibernate version:[/b] 3.0

[2]Mapping documents:[/b] I need them :-( from here

[3] Problem.

Following is the table structure i have for the parent child relation.


Table Name : Term

and following is the structure of it.
_ _ _ _ _ _ _ _ _ _ _ _ _
|Term_id Number PK
Term_text Varchar
Active_sw Varchar



There can be a parent child relation between the different terms and the data modeller represented it in the following way.

Table Name : Term_map

and following is the structure of it.

-----------------------------------------
|
|Parent_term_id Number PK,Fk1
|
|Child_term_id Number PK,Fk2
---------------------------------------------


now my problem is how do i do the mapping for the child elements of a parent..do i need 2 domain objects for this tables or would one be sufficient.


Is there a possible way of getting the hibernate mapping for this kind of table structure or do i need to ask the Data modeller to have everything in one table and have an other column for the parent_id?

please help.

Is there a reason you want to have a separate table to keep track of the relationships? Unless you are planning for this to be a many-to-many association (which really isn't a parent-child relationship), or if you're trying to be compatible with an existing database whose schema you can't change, it should be possible just to have a nullable "parent_id" foreign key field in the first (and in that case, only) table, in which case you can just follow the "Parent-child" example in the Hibernate manual almost verbatim.

I will try to convince the Datamodeller but in case if he doesnt agree..is there still away where we can map this 2 tables.

I believe what you're describing is a one-to-many relationship with a join table, as described here:
http://www.hibernate.org/hib_docs/v3/re ... l-join-12m

However, unlike the example provided there, you're using a self-referential association, i.e., the parent and child tables/classes are the same. I could be wrong, but I think the way to do this is to just do both the parent and child mappings within the same class. Something like this might work:



(I've left out the property mappings for the non-key fields for the sake of simplicity).

Note that I just copied the example from the above documentation page and changed it around to fit your scenario. I haven't actually tried doing something like this, so I'm not certain that it works. It should be worth a try, though.

Also note that this mapping treats Child_term_id as the primary key of the Term_map table. Unless you plan for a child to be able to have more than one parent, it isn't necessary for Parent_term_id to be part of the primary key.

I think what u r saying might really work...i still havnt tried it since we are still trying to convert the datamodel to the actual structure.

The questions i have is in the following why is it a many-to-many relation?it should be one-to-many right?

<class name="Term" table="Term">
<id name="id" column="Term_id">
<generator class="native"/>
</id>

<set name="children" table="Term_map">
<key column="Parent_term_id"/>
<many-to-many column="Child_term_id" unique="true" class="Term"/>
</set>


<join table="Term_map" inverse="true" optional="true">
<key column="Child_term_id"/>
<many-to-one name="parent" column="Parent_term_id" not-null="true"/>
</join>

</class>

To be honest, I was just copying what they had in the example. However, I believe the reason for it is that since you are using a join table, from a database point of view there's nothing stopping two different parent objects from claiming the same child as their own (which would happen if Term_map contained two rows with the same child_term_id). I think the unique="true" attribute is what actually makes it a one-to-many relationship.

Or it might just be a typo in the example. ;-)