Refs #28312 -- Added an optimized __bool__() to ModelChoiceIterator.

COUNT is more expensive than EXISTS; use the latter when possible.

django/forms/models.py

@@ -1145,6 +1145,9 @@ class ModelChoiceIterator:
         # and __len__() won't be called.
         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()
+
     def choice(self, obj):
         return (self.field.prepare_value(obj), self.field.label_from_instance(obj))
 

tests/model_forms/test_modelchoicefield.py

@@ -115,6 +115,17 @@ class ModelChoiceFieldTests(TestCase):
             (c4.pk, 'Fourth'),
         ])
 
+    def test_choices_bool(self):
+        f = forms.ModelChoiceField(Category.objects.all(), empty_label=None)
+        self.assertIs(bool(f.choices), True)
+        Category.objects.all().delete()
+        self.assertIs(bool(f.choices), False)
+
+    def test_choices_bool_empty_label(self):
+        f = forms.ModelChoiceField(Category.objects.all(), empty_label='--------')
+        Category.objects.all().delete()
+        self.assertIs(bool(f.choices), True)
+
     def test_deepcopies_widget(self):
         class ModelChoiceForm(forms.Form):
             category = forms.ModelChoiceField(Category.objects.all())