AW: AW: [sdo] ISSUE 165: Define behavior of DataObject.delete wrtChangeSummary

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

Hi Blaise,

 

If the behavior you describe is acceptable, then we can close this issue with no action.  The current wording is that change summary represents a diff between the old state and the new state, with created objects being objects that have entered the scope, and deleted objects being objects that left the scope.  What calls were used to achieve this doesn't enter into the equation.  By the way, do you agree with this definition of "create" and "delete"?  This is also something that is being discussed in the calls.

 

I think there is a general feeling in the group that this behaviour will be surprising to users.  Although the spec doesn't really say so, simply by calling a method named "delete" (as opposed to, say, "detach"), I think the user has signified an intention, namely, that he wishes the object be deleted from the data store.  And the worry is, that representing a delete/ reattach as a move, we are losing this intention.

 

The problem with the sentence you quote is that it doesn't say how this scenario is represented in the change summary, and I'm worried that users will expect it be represented as a delete and a create.  Perhaps the most backwards compatible way to  go is simply to clarify this in the spec.  Perhaps we should simply remove the sentence, that is, unless someone comes up with a use-case why the user would want to re-attach a deleted object.  We can leave the behaviour implementation dependent.  We all agree that most users don't reattach deleted objects.  And if the object is not reused, we already have the correct behavior: the object appears as deleted in the change summary.  If the user does a re-attach, he's on his own.

 

Ron

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Von: Blaise Doughan [mailto:blaise.doughan@oracle.com]
Gesendet: Donnerstag, 17. September 2009 16:38
An: Barack, Ron
Cc: sdo@lists.oasis-open.org
Betreff: Re: AW: [sdo] ISSUE 165: Define behavior of DataObject.delete wrt ChangeSummary

Hi Ron,

I'm still on leave, but these darn new phones make it too hard to leave work behind entirely.

If I delete an object, and then re-add it, as a user I would be surprised to get an error.  This use case is not nonsensical but it would be done rarely.

The spec is clear on this point, not sure why we would add in weasel words.  Is there a use case this line is preventing? 

-Blaise

On 2009-09-17, at 9:51 AM, "Barack, Ron" <ron.barack@sap.com> wrote:

Hi Blaise,

 

First off, welcome back, and best wishes on your "blessed event".

 

There's no doubt that the 2.1 spec allows, even encourages, deleted objects be reused in the graph. I just couldn't help but wonder why user would want to do such a thing.  Pooling was just a guess, because I can't think of anything else. 

 

The scenario you mention could also be handled with a detach.  The only difference is that with the delete, all non-readonly properties are reset.  If you're just moving something, that seems like an odd and confusing thing to do.  So why call delete?  If it's really desirable to reset the non-readonly properties too, then the user can of course do so himself.  But do you have a use-case for this?

 

My thinking is really to replace the statement you quote with something along that lines that it is a "user error" to reuse a deleted object, resulting in "undefined behavior".  This leaves implementations free to provide a backwards compatible option.  That maybe helps, but it doesn't change the fact that we are talking about breaking compatibility here.  On the other hand,

1)  I believe the functionality is nonsencical, and very rarely used (though I have no evidence of this)

2)  We can offer users the ability to achieve the same result using other means.

 

Best Regards,
Ron

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Von: Blaise Doughan [mailto:blaise.doughan@oracle.com]
Gesendet: Donnerstag, 17. September 2009 14:38
An: Barack, Ron
Cc: sdo@lists.oasis-open.org
Betreff: Re: [sdo] ISSUE 165: Define behavior of DataObject.delete wrt ChangeSummary

Hi Ron,

Based on the following statement, I never interpreted this as a means of implementing a pool of DataObjects, rather I took it to mean that I can put this deleted object back in the graph and it is now a modified rather than a deleted object (it maintains its object identity).  In other words a deleted object is not a dead object.

"A deleted DataObject can be used again, have its values set, and again be added into the data graph."

If this statement was removed, does that mean we need to guard against deleted objects being put back in the graph?  Possibly throwing an exception, this would be a backwards compatibility issue.

-Blaise

Barack, Ron wrote:

1BC7B594EE497146B0CFF2F493B6823406C6D07382@DEWDFECCR02.wdf.sap.corp type="cite">

RAISED BY: Ron

ChangeSummary is defined as a diff between the state of the graph when beginLogging was called, and the state when endLogging was called. The API used to modify the graph does not enter into the the definition.

Users that call DataObject.delete expect for the object to be represented in the change summary as a deleted object. Usually, that is what they get. But the description of the delete method seems to suggest that delete is rather more intended for implementing a pool of DataObjects, that are freed and later re-used in the graph. If delete is used in this way, it is possible that the "deleted" object appears as a modified object in the change summary.

PROPOSAL:
The utility of implementing object pools is questionable to say the least. It seems more reasonable to say that the delete method is intended to indicate the object should be deleted...as opposed to detach, which is a step towards moving the object.

 

http://www.osoa.org/jira/browse/SDO-165