I was looking at the Django-created database structure for my project
in a tool that shows all the foriegn-key relationships with nice
little lines (aka ER diagram). It looked very sparse. Most of my
relationships weren't showing up.
A little digging shows me that MySQL (windows, 5.0, InnoDB tables)
ignores the "REFERENCES" clause on a column. The only foreign keys it
was creating were the ones listed as "pending_references" in
management.py- that is, foreign key references created by altering the
original table after the referred-to table was created.
It was easy enough for me to add "FOREIGN KEY" clauses in
management.py and I was going to submit a patch, but I hit an issue.
Either I've hit a case that's not being tested, or no database checks
that the REFERENCES field points to an existing table...
My project has two apps, like so:
app1.models:
from app2.models import Zinger
class Review(models.Model):
critique = models.TextField
zinger = models.ManyToMany(Zinger)
app2.models:
class Zinger(models.Model):
wit = models.TextField
speaker = models.CharField(maxlength=80)
management.py creates the tables for the app that comes first
alphabetically, so it makes Foo and Foo's many-to-many table before
app2_zinger appears.
And, django/core/management.py creates the SQL for Foo's many-to-many
table assuming both the referred-to tables already exist. It doesn't
have access to the "already created" list nor a way to add to pending
references. Since MySQL is ignoring the REFERENCES, there's no
problem, but when I add FOREIGN KEY, I can't "syncdb" anymore.
I'm thinking I should write a django test like my foo/zinger example
above (with better names, perhaps). Where would it go? Presumably
somewhere under tests/modeltests?
Also, if I want to make _get_many_to_many_sql_for_model add FOREIGN
KEY constraints should I:
a) pass in (known/seen/created)_models, and return pending_references?
b) create a Model on the fly and call get_sql_create on it? Or would
that be _get_sql_model_create, which also need a known_models in and
pending_references out...
c) ignore Foreign Key on many_to_many entirely, things will break if
the constraint's enforced
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