On Dec 15, 2009, at 9:30 PM, mdipierro wrote:
> Good catch! Uploading fix in trunk.
Would you explain the fix, please, to those of us who don't understand the
subtlety of it? Thanks.
>
> Massimo
>
> On Dec 15, 11:13 pm, jonfroehlich <jonfroehl...@gmail.com> wrote:
>> Although the web2py documentation (page 165) appears to imply that the
>> argument distinct can only be set to True or False, the gluon/sql.py
>> file reveals otherwise. From line 2871 of sql.py:
>>
>> distinct = attributes.get('distinct', False)
>> if distinct == True:
>> sql_s += ' DISTINCT'
>> elif distinct:
>> sql_s += ' DISTINCT ON %s' % distinct
>>
>> So, it appears as though the code is trying to support providing
>> specific field names with which to execute the DISTINCT ON expression
>> upon (the "elif distinct" part). I found a post about this from June
>> when it looks like the above code was first
>> proposed:http://groups.google.com/group/web2py/browse_thread/thread/cc6180d335....
>> The code, however, does not appear to be executing properly. Whether
>> distinct is set to True or, more importantly, whether it is set to a
>> field name, the "distinct == True" branch is still taken and the "elif
>> distinct" branch is never executed (unfortunately in my case). I could
>> be doing something wrong, so let me try to include the relevant
>> information.
>>
>> I have the following table:
>> db.define_table('sensor_health',
>> Field('deployment_site', 'string'),
>> Field('sensor_name', 'string'),
>> Field('sensor_started', 'datetime'),
>> Field('last_heard_from', 'datetime'),
>> Field('sampling_rate', 'double'),
>> Field('sensor_event_count', 'integer')
>> )
>>
>> When executing this query:
>> sensorHealthRows= db(db.sensor_health.deployment_site ==
>> deploymentSite).select(
>> db.sensor_health.sensor_name, db.sensor_health.sensor_started,
>> db.sensor_health.last_heard_from,
>> db.sensor_health.sampling_rate,
>> db.sensor_health.sensor_event_count,
>> orderby=(db.sensor_health.sensor_name|
>> ~db.sensor_health.sensor_started),
>> distinct=db.sensor_health.sensor_name)
>>
>> Which should be equivalent to this in PostgresSQL:
>> SELECT DISTINCT ON (sensor_health.sensor_name)
>> sensor_health.sensor_name, sensor_health.sensor_started,
>> sensor_health.last_heard_from, sensor_health.sampling_rate,
>> sensor_health.sensor_event_count
>> FROM sensor_health
>> ORDER BY sensor_health.sensor_name, sensor_health.sensor_started
>> DESC;
>>
>> I set a breakpoint in sql.py at line 2872 in Wing IDE and the code
>> does indeed follow the "distinct == True" branch even though I clearly
>> set "distinct = db.sensor_health.sensor_name" in my query. Here's the
>> even stranger part: using Wing IDE's Debug Probe, I could actually
>> play around with this a bit (a direct copy/paste from the output is
>> below). Notice that the type(distinct) is class 'gluon.sql.Field' and,
>> perhaps even more interesting, it appears as though distinct evaluates
>> to both True and False. What's going on here?
>>
>>>>> print distinct
>>
>> sensor_health.sensor_name>>> distinct == True
>>
>> <gluon.sql.Query object at 0x0393E510>>>> if distinct == True: print
>> "distinct is True"
>>
>> ...
>> distinct is True>>> if distinct == False: print "distinct is False"
>>
>> ...
>> distinct is False>>> type(distinct)
>>
>> <class 'gluon.sql.Field'>
>>
>> Thanks for your help!
>>
>> j
>
> --
>
> You received this message because you are subscribed to the Google Groups
> "web2py-users" group.
> To post to this group, send email to web...@googlegroups.com.
> To unsubscribe from this group, send email to
> web2py+unsubscr...@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/web2py?hl=en.
>
>
--
You received this message because you are subscribed to the Google Groups
"web2py-users" group.
To post to this group, send email to web...@googlegroups.com.
To unsubscribe from this group, send email to
web2py+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/web2py?hl=en.
