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table-per-subclass; 2 subclasses, an entity is both

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sflahave

Post subject: table-per-subclass; 2 subclasses, an entity is both

Posted: Mon Jan 31, 2005 7:43 pm

Newbie

Joined: Thu Dec 30, 2004 6:58 pm
Posts: 6

We've run into a problem with the table-per-subclass strategy. We have the following simple hierarchy:
External_Organization
Vendor (extends External Organization)
Manufacturer (extends External Organization)

Some External Organizations might be a Vendor AND a Manufacturer. Hibernate doesn't seem to like this.

We have created a table for each of these entities. Each table has as its key a column named ORG_ID.

How can we get this to work?

Here is our mapping:

Code:

<hibernate-mapping>

<class name="ExternalOrganization"
      table="EXTERNAL_ORG_TBL"
      lazy="false">
       
    <cache usage="nonstrict-read-write"/>

   <!-- Common id property. -->
   <id name="orgId"
      type="long"
      column="ORG_ID"
      unsaved-value="null">
      <generator class="sequence">
            <param name="sequence">ENTERPRISE_SEQ</param>
        </generator>
   </id>
    
    <version name="version" column="VERSION" />
    
    <!-- properties removed for brevity -->
                
    <!-- Vendor subclass mapping to its own table, normalized. -->
   <joined-subclass name="Vendor"
                table="VENDOR_TBL"
                lazy="false">

   <key  column="ORG_ID" />
        
        <!-- properties removed for brevity -->   
      
     </joined-subclass>
    
    <!-- Manufacturer subclass mapping to its own table, normalized. -->
   <joined-subclass name="Manufacturer"
                table="MANUFACTURER_TBL"
                lazy="false">
                     
        <key  column="ORG_ID" />
    
        <!-- properties removed for brevity--> 
                     
     </joined-subclass>

</class>

</hibernate-mapping>

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sflahave

Post subject:

Posted: Tue Feb 01, 2005 12:01 pm

Newbie

Joined: Thu Dec 30, 2004 6:58 pm
Posts: 6

just to add - I'm just hoping someone can comment on whether or not this WOULD be a problem. Shouldn't Hibernate be able to handle this situation?
Thanks...

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sflahave

Post subject:

Posted: Tue Feb 01, 2005 1:40 pm

Newbie

Joined: Thu Dec 30, 2004 6:58 pm
Posts: 6

I wrote a simple test case to illustrate what's happening. It's clearer to me know what's happening. Say Dell Computers, as an External Organization, is a Vendor AND a Manufacturer. In our DB, Dell Computers has the ORG_ID 47599.
When I run the following test case, I get the error shown below. I see that Hibernate naturally does not like to have 2 ExternalOrganization instances with the same Id.

Code:

public void testSetVendorAndManufacturer() throws Exception {
        Vendor vendor = vendorDAO.getVendorById(new Long(47599), false);
        Manufacturer manufacturer =    manufacturerDAO.getManufacturerById(new Long(47599), false);
        
        Item item = itemDAO.getItemById(new Long(47852), false);
        item.addVendor(vendor);
        item.setManufacturer(manufacturer);
    }

Here is the error:

Code:

There was 1 error:

1) testSetVendorAndManufacturer(us.mn.state.health.test.TestItem)java.lang.ClassCastException: us.mn.state.health.model.common.Vendor
at us.mn.state.health.dao.HibernateManufacturerDAO.getManufacturerById(HibernateManufacturerDAO.java:32)
at us.mn.state.health.test.TestItem.testSetVendorAndManufacturer(TestItem.java:205)
at 
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

If I change the order in which I try to load the Vendor and Manufacturer object (ie, try to load the Manufacturer first), I get the same ClassCastException except its on a Manufacturer instead (ie, trying to cast a Vendor into a Manufacturer).

Certainly others have run into this problem! Right? What are we doing wrong? Do we have to use composition in our subclasses instead of Aggregration/Inheritance?
We're hoping there's some Hibernate tricks we don't know about.. :)

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