Looks like the book is wrong -- according to the code, rows1 & rows2 simply
combines the records from each Rows object -- it does not find the
intersection.
Anyway, given your code, it looks like we would not expect any results in
the intersection of the two Rows objects, as the conditions of each query
are mutually exclusive (i.e., "waypoint" either equals X or Y). Of course,
if X == Y, then the two sets of Rows are identical, but I assume that isn't
generally the case.
If you do really have non-mutually-exclusive results, why not just generate
the intersection with the SQL query (i.e., query1 & query2)?
Also, note, you queries should use "==", not a single "=".
Anthony
On Tuesday, February 6, 2018 at 4:57:29 PM UTC-5, Dave S wrote:
>
> 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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