I have an application (used for comparing routes) with 2 tables relevant to
this question. (Paraphrasing; code is at home,
where the router jammed.)
db.define_table('run',
Field('when', 'date'),
Field('description', 'string))
db.define_table('segment',
Field('waypoint', 'string'),
Field('timeofday', 'time'),
Field('odometer', 'decimal'),
Field('partof', 'reference run'))
I wanted to find the runs that had X as a waypoint and also had Y as a
waypoint, so I looked at
<URL:http://web2py.com/books/default/chapter/29/06/the-database-abstraction-layer#Combining-rows>
and wrote:
def fromto():
# not shown -- X and Y from request.vars
q1 = db.segment.waypoint = X
q2 = db.segment.waypoint = Y
runs1 = db(run.id == segment.partof & q1).select(...,distinct=True)
runs2 = db(run.id == segment.partof & q2).select(...,distinct=True)
theruns = runs1 & runs2
print len(runs1) + len(runs2) + len(theruns)
return ("runs" = theruns)
For the first waypoints I tried, the print produced counts of 111 10 121
which is clearly NOT the intersection. (I have verified that theruns
includes runs where Y is not included,
and the page shows the Y runs at the end of the X runs (that is, appended).)
If I go for union ('|' in line 7), the counts are 111 10 112.
(1 Y run did not go through X).
I add the "distinct=True" after the first attempt, in case multiple
appearances of a row was confusing things. It made no apparent difference.
I think this is on 2.14.6; I may be able to test newer web2py's tonight.
Am I doing something wrong, or was there a hiccup in intersection?
Dave S
/dps
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