ISSUE 130: New DataObject method: cast()

["Barack, Ron" <ron.barack@sap.com>]

http://www.osoa.org/jira/browse/SDO-130 

Hi Frank,

I had a little trouble entering this into the JIRA:  you make a proposal without stating what problem you would like to solve.  Casting to Node isn't part of the proposal, so XMLFidelity isn't addressed, so what is the problem we are trying to solve?  From your text I have extrapolated the following DESCRIPTION:

Under SDO 2.1, clients obtain a reference to the static SDO by casting the DataObject, that is, the static SDO must be the same instance as the DataObject.  This will be a problem when we do JPA/ JAXB integration.

Is this correct?

Now for some questions:

1) don't we need a symetric operation, one that allows you to go from the static SDO back to the DataObject (casting always worked in both directions)?

2) what is your justification is for the last assertion, that we need this for JPA/ JAXB integration?

3) Regarding casting to Node...Assuming we get JAXB integration to work (by the way, I think JAXB integration is much harder than JPA), doesn't that give us all the XMLFidelity we need?  Which technology should we focus on integrating?



Best Regards,
Ron

-----Ursprüngliche Nachricht-----
Von: Frank Budinsky [mailto:frankb@ca.ibm.com] 
Gesendet: Donnerstag, 12. Juni 2008 00:06
An: sdo@lists.oasis-open.org
Betreff: [sdo] [NEW ISSUE] New DataObject method: cast()

Hi Guys,

I would like to propose adding the following method to the DataObject 
interface:

    <T> T cast(Class<T> targetClass)

I'm not sure if the name should really be "cast" or "project" or something 
else, but I'm thinking "cast" may be best, since the intent is to get some 
other interface to work with and view the DataObject.

An implementation of this method will look something like this:

    public <T> T cast(Class<T> targetClass)
    { 
        if (targetClass.isInstance(this)) return (T)this;
        if (targetClass == Sequence.class && getType().isSequenced() 
return getSequence();
        // TBD other required or optional casts (e.g., maybe Node.class)
        // TBD implementation specific casts
        return null; //TBD maybe instead we should throw 
ClassCastException
    }

The idea behind this method is that it provides a single API for 
converting a DataObject to any other possible interface "view".

To get the Sequence view of a DataObject, a user would call:

    Sequence sequence = myDO.cast(Sequence.class);

To get the interface of a static SDO, you would call:

    Company company = myDO.cast(Company.class);

Using this API instead of simply using Java cast - (Company)myDO - has the 
advantage that we've opened up the door for different implementations of 
static SDO (e.g., a corresponding POJO) in the future where the static 
object and the DataObject are not required to be the same instance. This 
will be important when we get to the JAXB/JPA integration discussions.

Once this API is in place, we can think about other (required or optional) 
uses for it, such as using it to cast to Node.class (or something else) as 
a catch all for the XML Fidelity corner cases that we don't want to handle 
in SDO directly.

If we agree to add this new method, I think we should also deprecate 
getSequence(), which will have the added benefit of this issue not 
actually increasing the number of methods in the DataObject interface.

Thanks,
Frank.

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