orderby='<random>' on Google App Engine

[Albert Abril]

Hi!

As said on the book, in a DAL select, orderby='<random>' is not supported on GAE.

http://web2py.com/book/default/chapter/06#orderby,-groupby,-limitby,-distinct

Someone knows the best way to randomize a Rows dictionary?

(thinking in GAE deployment of course)

Thanks in advance.

[mdipierro]

import random
...
rows=db(...).select().sort(lambda row: random.random())

On Dec 6, 4:09 pm, Albert Abril <albert.ab...@gmail.com> wrote:
> Hi!
>
> As said on the book, in a DAL select, orderby='<random>' is not supported on

> GAE.http://web2py.com/book/default/chapter/06#orderby,-groupby,-limitby,-...

[Albert Abril]

I didn't know i could use imports in GAE

Thank you Massimo.

[mdipierro]

and you can put your own modules in web2py/site-packages and they will
be deployed with your app.

On Dec 6, 5:16 pm, Albert Abril <albert.ab...@gmail.com> wrote:
> I didn't know i could use imports in GAE
> Thank you Massimo.
>

[cjrh]

On Dec 7, 1:16 am, Albert Abril <albert.ab...@gmail.com> wrote:
> I didn't know i could use imports in GAE
> Thank you Massimo.

Book updated to reflect Massimo's answer. I thought it best to
emphasize the technique of using imports in these situations.

[blackthorne]

I don't see howcome this works as random sorting.
The only random thing I see it's the row chosen for sorting which will
only change the sorting criteria for the number of rows in the table.

Am I wrong?

P.S.:
I couldn't make a quick test because:
isco-Ribeiros-MacBook-Pro-2:web2py blackthorne$ python web2py.py -S
"test"
web2py Enterprise Web Framework
Created by Massimo Di Pierro, Copyright 2007-2010
Version 1.89.5 (2010-11-21 16:03:13)
Database drivers available: SQLite3
application test does not exist, create (y/n)?yes
Traceback (most recent call last):
File "web2py.py", line 23, in <module>
gluon.widget.start(cron=True)
File "/Users/blackthorne/Code/web2py/gluon/widget.py", line 766, in
start
File "/Users/blackthorne/Code/web2py/gluon/shell.py", line 166, in
run
NameError: name 'aidr' is not defined

?

[mdipierro]

You have an old version. aidr is a type fixed some time ago.

[blackthorne]

Seems to be 1.89.5 (2010-11-21 16:03:13)..

but what about my comment of the random sorting?

[mdipierro]

Not sure I understand our comment:

rows=db(...).select().sort(lambda row: random.random())

sorts the rows that have been already fetched at the web2py/python
level. That is all. What is wrong with it?

[Richard]

I think he's after an database-side implementation. If you used limit
and random together then wouldn't you always get the same set of data,
rather than random?

[mdipierro]

He asked: "Someone knows the best way to randomize a Rows dictionary?"

The proposed solution randomized the Rows object that you already
fethed form the db. You are correct that it does not fetch random
rows.

[Albert Abril]

Massimo is correct, 

I just wanted to know the more efficient way to randomize a Rows dictionary, instead of using orderby=<random>.

Because as said on the book, orderby=<random> is not supported on GAE.

Just easy as using python random library :)

Thanks again.

[Richard]

ah OK. 

Anyway, how could this be done server-side when also using limit? I want to show some random records without querying all the data.

[howesc]

as far as i know you would have to write some custom big table queries (not using web2py dal).  but in theory you could:
 - write a direct query to get all the keys of a table (and no data)
 - cache those keys
 - randomly choose a set of keys from the full list
 - write a google key query.

google is not really set up for selecting random data...

cfh

[Bruno Rocha]

Isn't random sort suported in GAE ?

rows = db(query).select().sort(lambda row: random.random())
File "/base/data/home/apps/s~movucahq/0-1.354917246392574252/gluon/dal.py", line 5789, in select
return self.db._adapter.select(self.query,fields,attributes)
File "/base/data/home/apps/s~movucahq/0-1.354917246392574252/gluon/dal.py", line 3410, in select
(items, tablename, fields) = self.select_raw(query,fields,attributes)
File "/base/data/home/apps/s~movucahq/0-1.354917246392574252/gluon/dal.py", line 3367, in select_raw
filters = self.expand(query)
File "/base/data/home/apps/s~movucahq/0-1.354917246392574252/gluon/dal.py", line 3249, in expand
return expression.op(expression.first, expression.second)
File "/base/data/home/apps/s~movucahq/0-1.354917246392574252/gluon/dal.py", line 3263, in AND
a = self.expand(first)
File "/base/data/home/apps/s~movucahq/0-1.354917246392574252/gluon/dal.py", line 3249, in expand
return expression.op(expression.first, expression.second)
File "/base/data/home/apps/s~movucahq/0-1.354917246392574252/gluon/dal.py", line 3109, in OR
def OR(self,first,second): raise SyntaxError, "Not supported" 
SyntaxError: Not supported 

--

Bruno Rocha

[http://rochacbruno.com.br]

[howesc]

looks like the exception there is because your query has an OR condition in it, which is not supported on GAE.  that sort should be in-memory and should work fine.

[Bruno Rocha]

On Fri, Nov 25, 2011 at 11:46 PM, howesc <how...@umich.edu> wrote:

looks like the exception there is because your query has an OR condition in it, which is not supported on GAE.  that sort should be in-memory and should work fine.

I found, the error was because of the use of contains() in query