#30317: model_to_dict() makes separate db calls for each missing field
------------------------------------------------+------------------------
Reporter: Chris Hranj | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Forms | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Currently, if a `model_to_dict` is called on a model instance that does
not already contain all of its fields (as a result of a `.only()`, etc),
it will make an individual database call for every single missing field
when attempting to access it, unless the `fields` argument is passed and
happens to contain only fields from the `.only()` used to query the object
originally.
The following example explains it more clearly (I'm using shell_plus
(https://django-extensions.readthedocs.io/en/latest/shell_plus.html) to
see the database interactions):
{{{
>>> from django.forms.models import model_to_dict
>>> sample_book = Book(
... title='Some Book',
... author='Jane Doe',
... description='A good book.',
... publisher='ABC Publishing',
... some_field='some text',
... some_other_field='some more text',
... )
>>> sample_book.save()
INSERT INTO "books_book" ("title", "author", "description", "publisher",
"some_field", "some_other_field")
VALUES ('Some Book', 'Jane Doe', 'A good book.', 'ABC Publishing', 'some
text', 'some more text')
Execution time: 0.001141s [Database: default]
>>> book = Book.objects.only('title').first()
SELECT "books_book"."id",
"books_book"."title"
FROM "books_book"
ORDER BY "books_book"."id" ASC
LIMIT 1
Execution time: 0.000123s [Database: default]
>>> model_to_dict(book)
SELECT "books_book"."id",
"books_book"."author"
FROM "books_book"
WHERE "books_book"."id" = 3
Execution time: 0.000098s [Database: default]
SELECT "books_book"."id",
"books_book"."description"
FROM "books_book"
WHERE "books_book"."id" = 3
Execution time: 0.000149s [Database: default]
SELECT "books_book"."id",
"books_book"."publisher"
FROM "books_book"
WHERE "books_book"."id" = 3
Execution time: 0.000067s [Database: default]
SELECT "books_book"."id",
"books_book"."some_field"
FROM "books_book"
WHERE "books_book"."id" = 3
Execution time: 0.000064s [Database: default]
SELECT "books_book"."id",
"books_book"."some_other_field"
FROM "books_book"
WHERE "books_book"."id" = 3
Execution time: 0.000062s [Database: default]
}}}
Ideally, this should make fewer (or just one) database calls if there are
missing fields.
Please let me know if this would be a welcome/worthwhile optimization. I
would love to work on it, as I've never contributed to django before and I
would really like to. Thank you!
--
Ticket URL: <https://code.djangoproject.com/ticket/30317>
Django <https://code.djangoproject.com/>
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