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From Pawel Veselov <pawel.vese...@gmail.com>
Subject Re: Removal of unnecessary "Order By" clauses
Date Wed, 29 Feb 2012 20:45:34 GMT
On Wed, Feb 29, 2012 at 12:06 PM, Pinaki Poddar <ppoddar@apache.org> wrote:

> > Extra performance cost that comes as a price for just wanting to use List
> API.
> That is not a sound argument.
>

I would compare this to coming into a store, and selecting between alarm
clocks. There is a $9.99 clock that displays time and beeps for alarm, and
there $49.99 clock that does the same plus auto-adjusts the time, has
FM/AM/CD/Sattelite receivers, and makes you coffee. The thing is that I
only wan the auto-adjust feature, and nothing else, but I'm placed in a
position that if I do want it, I have to get a fully loaded one, and pay
the maximum price.

Firstly, a performance cost is not a bug.
> Secondly, a feature i.e. to have List maintain order, it is natural that a
> provider will need some code and code costs. But that cost can not be
> termed
> as a performance cost. That is a feature cost.
>

There is a cost to maintain order across a single context, and a [much?]
higher cost to maintain order across contexts. Users are forced to pay
higher cost, even if all they want is a simpler feature. This is
effectively paying for stuff you don't need because of the stuff you do
need. And the spec seems to agree, saying that you if all you did is
requested the simpler feature (declared your collection as a List), you are
are not entitled to get a more advanced behavior (maintaining order across
contexts), and if you do, you have to explicitly request for that.


>
> With current capabilities of OpenJPA, a user determines and has complete
> control on whether s/he wants Set or List to represent a domain model
> properties.  If a user does use List API it means s/he requires ordering
> semantics. And that declaration is sufficient for OpenJPA to maintain
> element ordering for him/her. So what is the confusion about "just wanting
> to use List API"?
>
>
I [might] want to use List API to make calls like get(int), and use list
iterators that allow me to traverse the list both ways. I do care that the
order of elements doesn't change between me creating iterators of a the
same list, or accessing items in the same list (so get(i) always returns
the same object). It doesn't mean that I want and/or care for the framework
to guarantee all that across persistent contexts. If I did, I would specify
@Order? annotation.

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