Filtering OR-combined queries

Hi,

I have a query which ORs some selects on a single table together like this:

jurisdiction = 'aaa'
qs = Buss.objects.filter(jurisdiction=jurisdiction)
qs = qs | Buss.objects.filter(jurisdiction='xxx').exclude(name__in=qs.values_list('name', flat=True))
qs = qs | Buss.objects.filter(jurisdiction='yyy').exclude(name__in=qs.values_list('name', flat=True))

This seems to work just fine (and the raw SQL looks suitably complicated):

SELECT "paiyroll_buss"."id", "paiyroll_buss"."jurisdiction", "paiyroll_buss"."name", "paiyroll_buss"."description" FROM "paiyroll_buss" WHERE ("paiyroll_buss"."jurisdiction" = aaa OR ("paiyroll_buss"."jurisdiction" = xxx AND NOT ("paiyroll_buss"."name" IN (SELECT U0."name" FROM "paiyroll_buss" U0 WHERE U0."jurisdiction" = aaa))) OR ("paiyroll_buss"."jurisdiction" = yyy AND NOT ("paiyroll_buss"."name" IN (SELECT U0."name" FROM "paiyroll_buss" U0 WHERE (U0."jurisdiction" = aaa OR (U0."jurisdiction" = xxx AND NOT (U0."name" IN (SELECT U0."name" FROM "paiyroll_buss" U0 WHERE U0."jurisdiction" = aaa))))))))

Now, if I post-filter qs using something other than "aaa" (the first term above) like this:

   qs.filter('xxx)

then the resulting SQL has an 'AND "paiyroll_buss"."jurisdiction" = xxx' as one might expect. However, if I try to post-filter qs like this:

    qs.filter('aaa') # 'aaa' was the first term in the original trio of clauses

Then the formed SQL looks like this:

SELECT "paiyroll_buss"."id", "paiyroll_buss"."jurisdiction", "paiyroll_buss"."name", "paiyroll_buss"."description" FROM "paiyroll_buss" WHERE ("paiyroll_buss"."jurisdiction" = aaa OR ("paiyroll_buss"."jurisdiction" = xxx AND NOT ("paiyroll_buss"."name" IN (SELECT U0."name" FROM "paiyroll_buss" U0 WHERE U0."jurisdiction" = aaa))) OR ("paiyroll_buss"."jurisdiction" = yyy AND NOT ("paiyroll_buss"."name" IN (SELECT U0."name" FROM "paiyroll_buss" U0 WHERE (U0."jurisdiction" = aaa OR (U0."jurisdiction" = xxx AND NOT (U0."name" IN (SELECT U0."name" FROM "paiyroll_buss" U0 WHERE U0."jurisdiction" = aaa))))))))

i.e. just like the original 3-clause query. (I realise that in this case, the query degenerates to the first term). What am I missing?

Any clues appreciated.

Thanks, Shaheed

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