problem loading interfaces

kattavijay · **Joined:** Fri Sep 18, 2009 7:58 am **Posts:** 4

Hi, I have 3 tables in our db.
TABLE: Node(ID, StatusId, Type)
1, 1, S
2, 1, E

TABLE: Start(startID, departure)
1 10:00

TABLE: End(endID, arrival)
1 18:00

Code:

public class Node {
   int nodeId;
   Status status;
}
publilc interface Status {
  // marker interface
}
public class Start implements Status {
   int startId;
   Time departure;
}
public class End implements Status {
   int endId;
   Time arrival;
}

How to map status in node.hbm.xml based on the NodeType

Froestel · **Posted:** Sun Sep 20, 2009 4:35 am

Hi kattavijay,

I think you have to make Status an entity - map it itself. Then, it can be referenced by other entities. I guess you'd need a reference to an existing instance which will be of the type of an implementing class. You might - if possible - turn the interface into an abstract class and let it do the ID handling for all of its sub-classes.

CU
Froestel

P.S.: It would be very nice if you'd enclose your code snippets in BBCode Code-Tags (see the buttons below the subject field) for better readability.

kattavijay · **Joined:** Fri Sep 18, 2009 7:58 am **Posts:** 4

Hi,
the implementations of Status.java generate their own ids. the ids are generated by different front-ends, so I can not move id to Status.java. The only way to load status is based on the field nodetype.

Froestel · **Posted:** Sun Sep 20, 2009 6:21 am

Hi kattavijay,

if you require shared references to single instances of Status map the class to become an entity. Otherwise you might map it as a <component> (see Hibernate documentation, Sec. 5.1.15 http://docs.jboss.org/hibernate/stable/core/reference/en/html/mapping.html#mapping-declaration-component and Sec. 8 http://docs.jboss.org/hibernate/stable/core/reference/en/html/components.html) of your Node entity.

CU
Froestel

kattavijay · **Joined:** Fri Sep 18, 2009 7:58 am **Posts:** 4

Hi,
thanks for the reply.
My problem is not whether to map Status as entity or component. but how to load that entity/component. i mean based on the NodeType hibernate has to instantiate and load either Start or End from their respective tables.

Froestel · **Posted:** Sun Sep 20, 2009 10:29 am

Hi kattavijay,

Quote:

load either Start or End from their respective tables

Ah, I think now I understood your problem.

You need to map Start and End as sub-classes of Status. There are three strategies provided (see http://docs.jboss.org/hibernate/stable/core/reference/en/html/inheritance.html). I guess - as long as there are no additional classes extending Start and End any further (which is also possible, don't get me wrong) - then Table per subclass looks appropiate for your case.

A <many-to-one> mapping with the Node mapping targeting the Status entity should do it. Hibernate takes care of the polymorphism stuff then.

CU
Froestel

kattavijay · **Joined:** Fri Sep 18, 2009 7:58 am **Posts:** 4

Hi,
I can't use table per sub-class strategy as I don't have a status table.
I only have Start and End tables with their own id generators i.e. both the tables could have same ids.
I think I could use table per concrete class (using implicit polymorphism) strategy. so I have a mapping like this. But,

<class name="Start" table="Start">
<id name="id" type="int" column="startID">
<generator class="native"/>
</id>
<property name="departure" type="String" column="departure"/>
</class>

<class name="End" table="End">
<id name="id" type="int" column="endID">
<generator class="native"/>
</id>
<property name="arrival" type="String" column="arrival"/>
</class>

<class name="Node" table="Node">
<id name="id" type="int" column="ID">
<generator class="native"/>
</id>
<property name="nodeType" type="String" column="Type"/>
<many-to-one name="status" column="statusID" class="Status">

</class>

I dont necessarily need to load Status.java, is it possible to load Start.java for Type="Start" and End.java for Type="End"