Re: limiting the amount of objects retrieved

John Lenton <[email protected]> wrote:
> On Fri, Feb 06, 2004 at 05:15:09PM +0100, Sebastien Bigaret wrote:
> > 
> > John Lenton <[email protected]> wrote:
> > > I need (or, rather, would like) to be able to use the 'splice
> > > parameters' that I see commented out in Modeling.EditingContext to be
> > > able to send feedback to the user as to how many objects have been
> > > retrieved (and to let her cancel the operation if necessary). Is there
> > > anything left to be done to be able to use these parameters?
> > 
> >   A patch was once made for using slice parameters; I was not able to
> >   find it on sf.net, however if you're interested in testing it I can
> >   make it available on sf tonite after I'm back home.
> 
> I would be more than happy to do that, thank you.
> 
> > If the goal is simply to control that not too much objects are fetched
> > by a query, you may want to use ec.fetchCount() [same API as ec.fetch()]
> > which returns the number of objects fetched (without actually fetching
> > them).
> 
> yes, but it's more than that: I want to give the user detailed
> feedback as to the progress of the query, and the ability to cancel
> it. The easyest way to do both is using fetchCount and then fetching
> up to a number of objects.

  Fine, so the patch is for you! Sorry for the delay, it took me some
time to retrieve it --it was hidden in a dark corner of my hard-disk :)
It also required some work since it was made quite a long time ago and
was completely out-of-sync.

  The patch #892454 should be applied to v0.9pre16. It adds fetch slices
  and, as an extra bonus, 'orderBy' parameter to ec.fetch().

  It can be found at:
https://sourceforge.net/tracker/index.php?func=detail&aid=892454&group_id=58935&atid=489337

Sort orderings are strings like '<attribute path> [<operator>]', where
operator can be 'asc' (ascending, default), 'desc' (descending), and
'iasc' and 'idesc' (case-insensitive asc. and desc)


Here are some examples:

    ec.fetch('Book', 'author.lastName != NULL',
             orderBy='author.lastName desc, price desc, title iasc')

    ec.fetch('Book', 'author.lastName != NULL', limit=2, offset=2)

    ec.fetch('Book', limit=2, page=1)


Those examples are taken from test_EditingContext_Global.py (after patch
has been applied), methods test_17_fetchSpecWithSortOrderings(),
test_18/18b_fetchSpecWithFetchLimit() to which you can refer for further
details (you'll find there the full API for slices and
FetchSpecification as well).

  About fetch slices: 'offset' begins at zero (zero is the first record
  in the result set), while 'page' begins at one (page one is the first
  page).


Current limitations are:

  - it is available/tested for Postgresql and MySQL only

  - parameter isDeep shouldn't be set w/ fetch slices and/or with sort
    orderings,

  - inserted (unsaved) objects will appear at the end of each result
    set when limit and/or orderBy is set.


Last note, the patch contains all changes that have been made since
0.9pre16. This shouldn't be a problem, but I prefered to be explicit
about that; see CHANGES and MIGRATION for the details.


  Enjoy ;) and thanks for your time testing this.

-- Sébastien.


PS: just before posting I wondered whether this hadn't been discussed
    once. And true! see here:
https://sourceforge.net/mailarchive/forum.php?thread_id=1687932&forum_id=10674
https://sourceforge.net/mailarchive/forum.php?thread_id=1688402&forum_id=10674
https://sourceforge.net/mailarchive/forum.php?thread_id=1755269&forum_id=10674

The last url contains (at end) a post from me explaining the patch in
more details (forget about the cvs branch however, it is now
closed). Yes, this was one year ago...



-------------------------------------------------------
The SF.Net email is sponsored by EclipseCon 2004
Premiere Conference on Open Tools Development and Integration
See the breadth of Eclipse activity. February 3-5 in Anaheim, CA.
http://www.eclipsecon.org/osdn