id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
30317	model_to_dict() makes separate db calls for each missing field	Chris Hranj	nobody	"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!"	Cleanup/optimization	closed	Forms	dev	Normal	wontfix			Unreviewed	0	0	0	0	0	0