The code contains: if distinct == True:
This code was designed so that distinct is True or False (that is what the docs say) and it works. Jon tried to put a db.table.field in it. Is happens that db.table.field==True is a Query object in web2py and query objects and not None therefore they evaluates always to true. Changing this to if distinct is True: fixes the problem. It is very subtle. massimo On Dec 15, 11:38 pm, Jonathan Lundell <[email protected]> wrote: > 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 <[email protected]> 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 [email protected]. > > To unsubscribe from this group, send email to > > [email protected]. > > For more options, visit this group > > athttp://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 [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/web2py?hl=en.
