From 70b0be281caa08a0b639acb73e3b9fe5f6e7d278 Mon Sep 17 00:00:00 2001
From: Charles Roelli <charles@aurox.ch>
Date: Fri, 1 May 2026 13:45:01 +0000
Subject: Fixed #31295 -- Avoid Select widget triggering additional query when
 using ModelChoiceIterator.

---
 django/forms/models.py                     | 41 +++++++++++++++++++++++-------
 django/forms/widgets.py                    |  6 ++++-
 tests/model_forms/test_modelchoicefield.py | 11 ++++++++
 3 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/django/forms/models.py b/django/forms/models.py
index 9686baa6f2..ac56a4df78 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -3,6 +3,7 @@ Helper functions for creating Form classes from Django models
 and database field objects.
 """
 
+from collections import deque
 from itertools import chain
 
 from django.core.exceptions import (
@@ -1438,16 +1439,30 @@ class ModelChoiceIterator(BaseChoiceIterator):
     def __init__(self, field):
         self.field = field
         self.queryset = field.queryset
+        self._deque = deque()
+
+        def generator():
+            if self.field.empty_label is not None:
+                yield ("", self.field.empty_label)
+            queryset = self.queryset
+            # Can't use iterator() when queryset uses prefetch_related()
+            if not queryset._prefetch_related_lookups:
+                queryset = queryset.iterator()
+            for obj in iter(queryset):
+                yield self.choice(obj)
+            # Reset the generator after it's exhausted so that it can
+            # be used again.
+            self.generator = generator()
+
+        self.generator = generator()
 
     def __iter__(self):
-        if self.field.empty_label is not None:
-            yield ("", self.field.empty_label)
-        queryset = self.queryset
-        # Can't use iterator() when queryset uses prefetch_related()
-        if not queryset._prefetch_related_lookups:
-            queryset = queryset.iterator()
-        for obj in queryset:
-            yield self.choice(obj)
+        return self
+
+    def __next__(self):
+        if self._deque:
+            return self._deque.popleft()
+        return next(self.generator)
 
     def __len__(self):
         # count() adds a query but uses less memory since the QuerySet results
@@ -1456,7 +1471,9 @@ class ModelChoiceIterator(BaseChoiceIterator):
         return self.queryset.count() + (1 if self.field.empty_label is not None else 0)
 
     def __bool__(self):
-        return self.field.empty_label is not None or self.queryset.exists()
+        return (
+            self.field.empty_label is not None or self._deque or self.queryset.exists()
+        )
 
     def choice(self, obj):
         return (
@@ -1464,6 +1481,12 @@ class ModelChoiceIterator(BaseChoiceIterator):
             self.field.label_from_instance(obj),
         )
 
+    def peek(self):
+        value = next(self.generator, None)
+        if value is not None:
+            self._deque.append(value)
+        return value
+
 
 class ModelChoiceField(ChoiceField):
     """A ChoiceField whose choices are a model QuerySet."""
diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index 1bcfeba288..82685a3fea 100644
--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -851,7 +851,11 @@ class Select(ChoiceWidget):
         if self.allow_multiple_selected:
             return use_required_attribute
 
-        first_choice = next(iter(self.choices), None)
+        first_choice = (
+            self.choices.peek()
+            if hasattr(self.choices, "peek")
+            else next(iter(self.choices), None)
+        )
         return (
             use_required_attribute
             and first_choice is not None
diff --git a/tests/model_forms/test_modelchoicefield.py b/tests/model_forms/test_modelchoicefield.py
index 40c625da7c..f2f75829d1 100644
--- a/tests/model_forms/test_modelchoicefield.py
+++ b/tests/model_forms/test_modelchoicefield.py
@@ -169,6 +169,17 @@ class ModelChoiceFieldTests(TestCase):
         Category.objects.all().delete()
         self.assertIs(bool(f.choices), False)
 
+    def test_empty_label_one_query(self):
+        class MyForm(forms.Form):
+            f = forms.ModelChoiceField(Category.objects.all(), empty_label=None)
+
+        form = MyForm()
+        with self.assertNumQueries(1):
+            form.as_ul()
+        # Make sure the query re-runs when re-rendering the form.
+        with self.assertNumQueries(1):
+            form.as_ul()
+
     def test_choices_bool_empty_label(self):
         f = forms.ModelChoiceField(Category.objects.all(), empty_label="--------")
         Category.objects.all().delete()
-- 
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