Allow in_bulk() for fields with UniqueConstraint

Previously, in_bulk() required fields to have unique=True. Now, fields with an unconditional UniqueConstraint are also supported, enabling lookups like in_bulk(field_name="slug") for such fields.

Fixes issue where fields unique via UniqueConstraint could not be used with in_bulk().

django/db/models/query.py

@@ -17,6 +17,7 @@ from django.db import (
 )
 from django.db.models import AutoField, DateField, DateTimeField, sql
 from django.db.models.constants import LOOKUP_SEP
+from django.db.models.constraints import UniqueConstraint
 from django.db.models.deletion import Collector
 from django.db.models.expressions import Case, Expression, F, Value, When
 from django.db.models.functions import Cast, Trunc
@@ -689,8 +690,19 @@ class QuerySet:
         """
         assert not self.query.is_sliced, \
             "Cannot use 'limit' or 'offset' with in_bulk"
-        if field_name != 'pk' and not self.model._meta.get_field(field_name).unique:
-            raise ValueError("in_bulk()'s field_name must be a unique field but %r isn't." % field_name)
+        if field_name != 'pk':
+            # Check if field is unique via field.unique or UniqueConstraint
+            field = self.model._meta.get_field(field_name)
+            if not field.unique:
+                # Check if field has a total UniqueConstraint (single field, no condition)
+                is_unique_constraint = any(
+                    isinstance(constraint, UniqueConstraint) and
+                    constraint.fields == (field_name,) and
+                    constraint.condition is None
+                    for constraint in self.model._meta.constraints
+                )
+                if not is_unique_constraint:
+                    raise ValueError("in_bulk()'s field_name must be a unique field but %r isn't." % field_name)
         if id_list is not None:
             if not id_list:
                 return {}

tests/constraints/models.py

@@ -77,3 +77,13 @@ class AbstractModel(models.Model):
 
 class ChildModel(AbstractModel):
     pass
+
+
+class UniqueConstraintInBulkProduct(models.Model):
+    """Model for testing in_bulk() with UniqueConstraint on a single field."""
+    name = models.CharField(max_length=255)
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(fields=['name'], name='unique_name'),
+        ]

tests/constraints/tests.py

@@ -7,7 +7,7 @@ from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
 
 from .models import (
     ChildModel, Product, UniqueConstraintConditionProduct,
-    UniqueConstraintProduct,
+    UniqueConstraintInBulkProduct, UniqueConstraintProduct,
 )
 
 
@@ -238,3 +238,41 @@ class UniqueConstraintTests(TestCase):
     def test_condition_must_be_q(self):
         with self.assertRaisesMessage(ValueError, 'UniqueConstraint.condition must be a Q instance.'):
             models.UniqueConstraint(name='uniq', fields=['name'], condition='invalid')
+
+    def test_in_bulk_with_unique_constraint(self):
+        """Test that in_bulk() works with UniqueConstraint on a single field."""
+        # Create test objects
+        obj1 = UniqueConstraintInBulkProduct.objects.create(name='product1')
+        obj2 = UniqueConstraintInBulkProduct.objects.create(name='product2')
+        obj3 = UniqueConstraintInBulkProduct.objects.create(name='product3')
+
+        # Test in_bulk with field_name that has UniqueConstraint
+        result = UniqueConstraintInBulkProduct.objects.in_bulk(
+            ['product1', 'product2', 'product3'],
+            field_name='name'
+        )
+
+        self.assertEqual(len(result), 3)
+        self.assertEqual(result['product1'], obj1)
+        self.assertEqual(result['product2'], obj2)
+        self.assertEqual(result['product3'], obj3)
+
+    def test_in_bulk_without_id_list_with_unique_constraint(self):
+        """Test that in_bulk() works without id_list for UniqueConstraint fields."""
+        obj1 = UniqueConstraintInBulkProduct.objects.create(name='product_a')
+        obj2 = UniqueConstraintInBulkProduct.objects.create(name='product_b')
+
+        result = UniqueConstraintInBulkProduct.objects.in_bulk(field_name='name')
+
+        self.assertEqual(len(result), 2)
+        self.assertEqual(result['product_a'], obj1)
+        self.assertEqual(result['product_b'], obj2)
+
+    @skipUnlessDBFeature('supports_partial_indexes')
+    def test_in_bulk_with_partial_unique_constraint_fails(self):
+        """Test that in_bulk() fails for fields with conditional UniqueConstraint."""
+        UniqueConstraintConditionProduct.objects.create(name='p1')
+
+        msg = "in_bulk()'s field_name must be a unique field but 'name' isn't."
+        with self.assertRaisesMessage(ValueError, msg):
+            UniqueConstraintConditionProduct.objects.in_bulk(['p1'], field_name='name')