Complex query, queryset.query.alias_map and query changes

Hello folks!

I have a complex queryset here that do joins in at least 8 tables. The query is fast, but has use of Postgresql `concat` method, and to make it have correct aliases I'm using `qs.query.alias_map` where qs is my queryset instance:

def my_complex_queryset(self):      qs = self.filter(*lot_of_stuff_with_lot_of_joins)      alias_map = {
        j.table_name: a for a, j in qs.query.alias_map.items() 
            if j.table_name in ['table_a', 'table_b']
    }
    concat_str = (
        'concat("{table_a}"."city", "{table_a}"."state") '
        '!= concat("{table_b}"."city", "{table_b}"."state")'
    ).format(
        table_a=alias_map['table_a'],
        table_b=alias_map['table_b']
    )
    qs = qs.extra(where=[concat_str])
    return qs

The problem is when the query is re-executed with some other table in the joins because it will change the alias_map but won't run my method again to  update the concat_str:

my_qs = MyModel.objects.my_complex_queryset()  print my_qs  # now it will fail because alias changed:  print my_qs.filter(another_table_1__another_table_2__id__in=[1, 2, 3])

The error I receive is:

 ProgrammingError: invalid reference to FROM-clause entry for table "table_a"

LINE 1: ... AND U0."some_id" IN (13361, 9820) AND (concat("table_a...

                                                             ^

HINT:  Perhaps you meant to reference the table alias "u9".

The great question is: Is possible to do the query with dynamic aliases to be used in concat string? Maybe the `tables` argument to extra? I not saw much doc about it :\.

My Django version is 1.6.x, not because my choice but because software here still a bit legacy about Django versions and we won't change until January.

Thanks for your attention!

Felipe Prenholato.

Home page: http://devwithpassion.com | http://chronosbox.org/blog
GitHub: http://github.com/chronossc/ | Twitter: http://twitter.com/chronossc

LinkedIn: http://br.linkedin.com/in/felipeprenholato/

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