Save an EMF Resource with or without namespace!

  We tried out this one somewhere in 2007, but i suddenly felt the need to write about it now( i dono, funny like that!). Well coming to the point... serializing an EMF Resource to an XML file actually seems strange but sometimes it becomes necessary. I'll not get into the details of why do we need an XML file with no namespace! and just tell you how to do it.

  When an XML file is parsed using Resource API, for every XML element a corresponding model element is searched from an EPackage instance. This EPacakge instance is normally registered to an namespace URI. For eg. <myns:SHIPORDER>  XML element may map to an EClass ShipOrder in the model and myns URI is registered to an instance of ShipOrderPackage.  So when the SHIPORDER XML element is encountered Resource API understands that an object of type StudentType is to be created.

  Now, what if the XML element has no namespace... it'll look like this: . If we want to continue the usual way, then we have to do:

• Register the EPackage instance to an empty namespace URI.
  
• extend the XMLHelperImpl class and override getQName(EPackage, String, boolean) method
• bind this XMLHelper implementation to your model's generated XyzResouceImpl through createXMLHelper() method.

The first point is quite straight forward. Although its better to register ur EPackage instance to both empty as well as the required namespace URI. For the second one, you need to extend the class org.eclipse.emf.ecore.xmi.impl.XMLHelperImpl and override the method specified above to suit ur requirements. Here's an example (considering the good old ShipOrder schema model)

/**

 * let's save without namespace!

 * just delegate to appropriate Resouce API 

 *

 */

public class ShipOrderXMLHelper extends XMLHelperImpl {

protected String getQName(EPackage package1, String name,

boolean mustHavePrefix) 

{

   if( isNameSpaceNeeded() ) {

    // let's send what ever prefix that's got as the arguement

    return super.getQName(package1, name, true);

   }

   else {

    // i don't want a namespace prefix 

    return super.getQName(package1, name, false);

   }

            return "";

}

}

  Now that we have our implementation of XMLHelper, let's bind it to the generated ShipOrderResource implementation.

/**

 *

 * The Resource associated with the package.

 *

 * @see org.example.shiporder.util.ShiporderResourceFactoryImpl

 * @generated

 */

public class ShiporderResourceImpl extends XMLResourceImpl {

/* (non-Javadoc)

* @see org.eclipse.emf.ecore.xmi.impl.XMLResourceImpl#createXMLHelper()

* an override to bind our helper implementation

*/

protected XMLHelper createXMLHelper() {

return new ShipOrderXMLHelper();

}

    // other generated ShipOrderResouceImpl methods follow.        

} //ShiporderResourceImpl

   That's it you are all set to serialize an EMF resource without namespace. Before you go for a coffee ... one last thing ... do not forget to create ur EMF resource from the generated XyzResourceFactory.