Re: state checking

I currently have very very little time, so please excuse this too short
answer.

Duncan McGreggor <[email protected]> wrote:
> Hey folks,
> 
> I am aware that checking for changes in a database source data is not
> supported yet, but I am attempting to do this anyway...
>
> What I want to do is a fetch, and then operate on the data, then before I
> save the changes, fetch again to see if the source has changed at all. I
> have methods that do this, however... the data seems to be cached during the
> call to EditingContext(), as the fetch pulls the same data over and over,
> not matter how much I change the source data.

Fine! --> what you need here is (again!) definitely optimistic locking.

To answer your questions: yes, row snapshots are cached, and this leads
to the limitation you already noticed.  Is there an easy way to get a
fresh snapshot? Sorry, not in the current state.

I initially thought this was somewhere on a branch, but the recent
discussion we had with Ernesto proved that this only lies on my
hard-disk.  

  I believe that you want to go this way because you need it; same as
  for Ernesto.

I've put there a tarball containing the current state for optimistic
locking:
https://sourceforge.net/tracker/index.php?func=detail&aid=986122&group_id=58935&atid=489338

There's a patch against the current CVS head and some additional
files, full content is: 

    optimistic_locking.patch
    Modeling/DefaultEditingContextDelegate.py
    Modeling/EditingContextDefaultDelegate.py
    Modeling/interfaces/EditingContextDelegate.py
    Modeling/tests/test_EditingContext_optimistic_locking.py

I'm sorry I've not enough time to comment right now, but at least it is
functional; you can refer to the tests that are contained in module
test_EditingContext_optimistic_locking.py

  Hopefully this will be a good starting point for all of you needing
  the feature; please just keep in mind this is alpha software. Any
  feedbacks will be greatly appreciated!

Last: by now I cannot give a exhaustive overview of the current
limitations, however the tests comment some of these.  Plus, do not try
to make it work w/ nested ECs unless you know what you're doing (and
since I've no time to check this right now, I'd say I do not know what
sort of weird effects you can get if you try this with nested ECs!).

-- Sébastien.



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