Silly django confusion

24 April 2012 3:51 PM (python | django | coding)

I'm setting up a testing environment for work, using fixtures to save and load test data and I got a little stumped by something I ran into.

I had exported one of the database tables we use to a json file that I was going to import into a fresh new database to test with. When I imported it everything seemed fine, except when looking at the actual page. So this is what I found:

SELECT * FROM app_table;
    => 3 rows of data
from app.models import Table

    => 3

    => []

This is weird. So I looked at the django.db.connection.queries property and I realized that it was doing a join since the model subclasses another:

from django.db import models

from app.models import SuperTable

class Table(SuperTable):...

Which, of course, means that in order to get the complete Table instance, the related SuperTable instance is also required, but in order to do a COUNT of app_table it isn't necessary. And that's where the inconsistency came from, now that I've also copied the contents of SuperTable everything is fine again.

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