As the subject states, I am using the model-validation branch at the
moment, which allows me to do, well, validation in the models.
I've however, noticed a very strange behaviour of the validation
logic, - any time the clean() method is fired on the
"materialized" (saved or retrieved from the database) model, that
contains unique fields, the following query is fired (let me just give
you an example):
from django.db import models
class A(models.Model):
pass
a = A.objects.create()
a.clean()
a.clean() results, among everything, in this: 'SELECT (1) AS "a" FROM
"val_a" WHERE ("val_a"."id" = 1 AND NOT ("val_a"."id" = 1 ))'
I might be missing something vital, but what is that "where" clause
there for? What is it supposed to check? The stacktrace for the query
is the following:
787 clean django/db/models/base.py
619 validate django/db/models/base.py
624 validate_unique django/db/models/base.py
683 _perform_unique_checks django/db/models/base.py
112 __nonzero__ django/db/models/query.py
106 _result_iter django/db/models/query.py
692 _fill_cache django/db/models/query.py
756 iterator django/db/models/query.py
287 results_iter django/db/models/sql/query.py
2369 execute_sql django/db/models/sql/query.py
Apparently, it is happening inside the uniqueness check. Anyway, the
most strange thing, is that calling clean() results in a query. I've
noticed it when I was displaying a set of a few hundred objects (each
of them has to be cleaned before sending the data to template), which
resulted in a few hundred of queries (for a single request), which
brought my dev-machine to the knees. It becomes worse if the cleaned
model is a part of a table-inheritance hierarchy, - clean() is called
sequentially for every model "up" the hierarchy, which results in a
tremendous number of queries executed per single request.
I must say, however, that I, at this moment, have no idea how to check
for uniqueness *without* issuing a query and, from what I see, django
doesn't like to assume things, so the db hits *will* be made.
Obviously, I can swindle Django into not checking uniqueness on clean
(by rolling my own clean method in models.Model subclasses), however,
that doesn't sound like a very good idea (if alternatives exist).
Sorry if this is an inappropriate list/group for this question. Maybe
I should instead address it to the django-developers or the issue
tracker.
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