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#+TITLE: Silly django confusion
#+DESCRIPTION: Think about this next time...
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:
#+BEGIN_SRC sql
SELECT * FROM app_table;
=> 3 rows of data
#+END_SRC
#+BEGIN_SRC python
from app.models import Table
Table.objects.count()
=> 3
Table.objects.all()
=> []
#+END_SRC
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:
#+BEGIN_SRC python
from django.db import models
from app.models import SuperTable
class Table(SuperTable):
field1 = models.CharField(max_lenth=200)
#+END_SRC
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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