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
36372	refresh_from_db with explicit fields can't clear a relation by it's query name unless it's prefetched	Roman Donchenko		"Consider the following project:

`testapp/__init__.py`: empty
`testapp/models.py`:


{{{
from django.db import models
    
class Container(models.Model):
    pass

class Item(models.Model):
    container = models.ForeignKey(Container, on_delete=models.CASCADE)
}}}

`testapp/migrations/__init__.py`: empty
`testapp/migrations/0001_initial.py`:

{{{
# Generated by Django 5.2 on 2025-05-06 17:03

import django.db.models.deletion
from django.db import migrations, models


class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='Container',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
            ],
        ),
        migrations.CreateModel(
            name='Item',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('container', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='testapp.container')),
            ],
        ),
    ]
}}}

`test.py`:

{{{
import django
from django.conf import settings
from django.core import management

settings.configure(
    INSTALLED_APPS=[""testapp""],
    DATABASES={
      'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': ':memory:',
      },
    },
)
django.setup()

management.call_command(""migrate"")

from testapp.models import Container

Container.objects.create()

c = Container.objects.first()
# c = Container.objects.prefetch_related(""item_set"").first()
c.refresh_from_db(fields=[""item_set""])
}}}

Running `test.py` results in the following output:

{{{
Operations to perform:
  Apply all migrations: testapp
Running migrations:
  Applying testapp.0001_initial... OK
Traceback (most recent call last):
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/options.py"", line 683, in get_field
    return self.fields_map[field_name]
           ~~~~~~~~~~~~~~~^^^^^^^^^^^^
KeyError: 'item_set'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ""[...]/test.py"", line 24, in <module>
    c.refresh_from_db(fields=[""item_set""])
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/base.py"", line 737, in refresh_from_db
    db_instance = db_instance_qs.get()
                  ^^^^^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/query.py"", line 629, in get
    num = len(clone)
          ^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/query.py"", line 366, in __len__
    self._fetch_all()
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/query.py"", line 1935, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/query.py"", line 91, in __iter__
    results = compiler.execute_sql(
              ^^^^^^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/sql/compiler.py"", line 1609, in execute_sql
    sql, params = self.as_sql()
                  ^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/sql/compiler.py"", line 765, in as_sql
    extra_select, order_by, group_by = self.pre_sql_setup(
                                       ^^^^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/sql/compiler.py"", line 85, in pre_sql_setup
    self.setup_query(with_col_aliases=with_col_aliases)
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/sql/compiler.py"", line 74, in setup_query
    self.select, self.klass_info, self.annotation_col_map = self.get_select(
                                                            ^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/sql/compiler.py"", line 252, in get_select
    select_mask = self.query.get_select_mask()
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/sql/query.py"", line 885, in get_select_mask
    return self._get_only_select_mask(opts, mask)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/sql/query.py"", line 854, in _get_only_select_mask
    field = opts.get_field(field_name)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ""[...]/venv/lib/python3.12/site-packages/django/db/models/options.py"", line 685, in get_field
    raise FieldDoesNotExist(
django.core.exceptions.FieldDoesNotExist: Container has no field named 'item_set'
}}}

OTOH, if you uncomment the second-to-last line in `test.py`, there is no exception.

I would expect the `refresh_from_db` call to simply do nothing if the relation is not prefetched. This behavior is making it impossible to use this functionality unless you know for sure whether the relation is prefetched.
"	Bug	closed	Database layer (models, ORM)	5.2	Normal	wontfix		Mariusz Felisiak Simon Charette	Unreviewed	0	0	0	0	0	0