[Modeling-users] Fetching limited numbers of rows

[Kertis, Dennis]

Is there a way to tell Modeling to only fetch the first N rows? Ideally,
I'd like to be able to specify an offset and a count to do something like
paging results of a search.



Thanks,

Dennis

[Mario Ruggier]

Is there a way to tell Modeling to only fetch the first N rows? 
Ideally, I'd like to be able to specify an offset and a count to do
something like paging results of a search.
Thanks,
Dennis

Hi, there were a few discussions on this a while back, including a
pretty well-defined proposal to add offset and paging capabilities.
Sebastien had also worked on it in a branch, but I do not know what the
status of that is now. Search the mailing list archive for "offset"...
but the main thread about this was:

API cleanup proposal  
http://sourceforge.net/mailarchive/message.php?msg_id=5142917

limiting the amount of objects retrieved  
http://sourceforge.net/mailarchive/message.php?msg_id=7163083

limit
http://sourceforge.net/mailarchive/message.php?msg_id=4159154

mario

[Sebastien Bigaret]

Hi Dennis and all,

To all: if you're using the "Fetch slices and sort orderings" patch,
I need your feedback, see at end of msg.

Is there a way to tell Modeling to only fetch the first N rows?  Ideally,
I'd like to be able to specify an offset and a count to do something like
paging results of a search.

Thanks Mario for the references you posted, I appreciate not having to
search the archives ;)

As Mario already answered, there is a patch doing what you want
(offset and count in ec.fetch()) You'll find example in the announce,
hopefully you'll find this useful, and if you need more informations
then do not hesitate to ask.

Related announce is at:
http://sourceforge.net/mailarchive/message.php?msg_id=7163083
And the patch is at:
http://sourceforge.net/tracker/index.php?func=detail&aid=892454&group_id=58935&atid=489337

Hi, there were a few discussions on this a while back, including a pretty
well-defined proposal to add offset and paging capabilities. Sebastien had
also worked on it in a branch, but I do not know what the status of that is
now.

The status is: wait for comments ;) It seems that some of you out there
use this patch, could you please comment? In particular:

| 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. is the
| limitation of having inserted objects

Do you find this annoying? With which database adaptor(s) do you use
it? I'm asking this because it's out there for a long time, and it's
probably time to integrate it into the main trunk (geez, I can't
believe the original proposal was more than a year ago!)

-- Sébastien.

Search the mailing list archive for "offset"... but the main thread about
API cleanup proposal  
http://sourceforge.net/mailarchive/message.php?msg_id=5142917
limiting the amount of objects retrieved  
http://sourceforge.net/mailarchive/message.php?msg_id=7163083
limit
http://sourceforge.net/mailarchive/message.php?msg_id=4159154
mario

[John Lenton]

On 24 Aug 2004 23:14:05 +0200, Sebastien Bigaret

Post by Sebastien Bigaret
The status is: wait for comments ;) It seems that some of you out there
|
| - 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. is the
| limitation of having inserted objects
Do you find this annoying? With which database adaptor(s) do you use
it? I'm asking this because it's out there for a long time, and it's
probably time to integrate it into the main trunk (geez, I can't
believe the original proposal was more than a year ago!)

I'm using this patch in every single project I'm using Modeling in
(that is one standalone and three integrated in zope). Always with
postgres; if/when one of my customers needs support for this in
something else, I'll find a way for them to sponsor the development :)
(or if cimarrón/luca goes with sqlite, I'll do it on my own steam).

What I'm trying to say is that the first limitation isn't an issue for
me because postgres is my preferred database anyway; the third
limitation isn't really an issue because I have yet to come across a
use case where you insert an object and then request an ordered or
limited list of those same objects without having done a saveChanges
beforehand.

The second limitation comes as a surprise; trying it out, I see that
the problem is that isDeep performs two selects on the database,
instead of one; this is, I guess, so AdaptorChannel doesn't have to
know about it. However, the function needed in DataBaseContext to do
this merging, it seems to me, is SortOrdering's
__compareUsingKeyOrderArray__; the patch is obvious, but that function
has too many underscores for me to call it blithely from another
module. Also, doing it efficiently might be more complicated, because
each call to __compareUsingKeyOrderArray__ might be expensive as it
stands.