Fixed #25535 -- Made ForeignObject checks less strict.

Check that the foreign object `from_fields` are a subset of any unique
constraints on the foreign model.

1 files changed, 80 insertions, 3 deletions

diff --git a/tests/invalid_models_tests/test_relative_fields.py b/tests/invalid_models_tests/test_relative_fields.py
index ad1c25da52..545aa87548 100644
--- a/tests/invalid_models_tests/test_relative_fields.py
+++ b/tests/invalid_models_tests/test_relative_fields.py
@@ -5,6 +5,7 @@ import warnings
 
 from django.core.checks import Error, Warning as DjangoWarning
 from django.db import models
+from django.db.models.fields.related import ForeignObject
 from django.test import ignore_warnings
 from django.test.testcases import skipIfDBFeature
 from django.test.utils import override_settings
@@ -507,9 +508,9 @@ class RelativeFieldTests(IsolatedModelsTestCase):
         errors = field.check()
         expected = [
             Error(
-                "None of the fields 'country_id', 'city_id' on model 'Person' "
-                "have a unique=True constraint.",
-                hint=None,
+                "No subset of the fields 'country_id', 'city_id' on model 'Person' is unique",
+                hint="Add a unique=True on any of the fields 'country_id', 'city_id' of 'Person', "
+                     "or add them all or a subset to a unique_together constraint.",
                 obj=field,
                 id='fields.E310',
             )
@@ -1395,3 +1396,79 @@ class M2mThroughFieldsTests(IsolatedModelsTestCase):
                 obj=field,
                 id='fields.E337')]
         self.assertEqual(expected, errors)
+
+    def test_superset_foreign_object(self):
+        class Parent(models.Model):
+            a = models.PositiveIntegerField()
+            b = models.PositiveIntegerField()
+            c = models.PositiveIntegerField()
+
+            class Meta:
+                unique_together = (
+                    ('a', 'b', 'c'),
+                )
+
+        class Child(models.Model):
+            a = models.PositiveIntegerField()
+            b = models.PositiveIntegerField()
+            value = models.CharField(max_length=255)
+
+            parent = ForeignObject(
+                Parent,
+                on_delete=models.SET_NULL,
+                from_fields=('a', 'b'),
+                to_fields=('a', 'b'),
+                related_name='children',
+            )
+
+        field = Child._meta.get_field('parent')
+        errors = field.check(from_model=Child)
+        expected = [
+            Error(
+                "No subset of the fields 'a', 'b' on model 'Parent' is unique",
+                hint="Add a unique=True on any of the fields 'a', 'b' of 'Parent', or add them "
+                     "all or a subset to a unique_together constraint.",
+                obj=field,
+                id='fields.E310',
+            ),
+        ]
+        self.assertEqual(expected, errors)
+
+    def test_insersection_foreign_object(self):
+        class Parent(models.Model):
+            a = models.PositiveIntegerField()
+            b = models.PositiveIntegerField()
+            c = models.PositiveIntegerField()
+            d = models.PositiveIntegerField()
+
+            class Meta:
+                unique_together = (
+                    ('a', 'b', 'c'),
+                )
+
+        class Child(models.Model):
+            a = models.PositiveIntegerField()
+            b = models.PositiveIntegerField()
+            d = models.PositiveIntegerField()
+            value = models.CharField(max_length=255)
+
+            parent = ForeignObject(
+                Parent,
+                on_delete=models.SET_NULL,
+                from_fields=('a', 'b', 'd'),
+                to_fields=('a', 'b', 'd'),
+                related_name='children',
+            )
+
+        field = Child._meta.get_field('parent')
+        errors = field.check(from_model=Child)
+        expected = [
+            Error(
+                "No subset of the fields 'a', 'b', 'd' on model 'Parent' is unique",
+                hint="Add a unique=True on any of the fields 'a', 'b', 'd' of 'Parent', or add "
+                     "them all or a subset to a unique_together constraint.",
+                obj=field,
+                id='fields.E310',
+            ),
+        ]
+        self.assertEqual(expected, errors)