From 816b8d9518c41f034dcbacfd1f1826f2366975e5 Mon Sep 17 00:00:00 2001
From: Hasan Ramezani <hasan.r67@gmail.com>
Date: Thu, 3 May 2018 11:38:29 +0430
Subject: [PATCH] Fixed #29358 -- Added a system check to prohibit models with
 more than one primary_key field.

---
 django/db/models/base.py                  | 14 ++++++++++++++
 docs/ref/checks.txt                       |  1 +
 tests/invalid_models_tests/test_models.py | 13 +++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 9af6a8f92d..3573838b99 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -1189,6 +1189,7 @@ class Model(metaclass=ModelBase):
                 *cls._check_field_name_clashes(),
                 *cls._check_model_name_db_lookup_clashes(),
                 *cls._check_property_name_related_field_accessor_clashes(),
+                *cls._check_single_primary_key(),
             )
             errors.extend(clash_errors)
             # If there are field name clashes, hide consequent column name
@@ -1436,6 +1437,19 @@ class Model(metaclass=ModelBase):
                 )
         return errors
 
+    @classmethod
+    def _check_single_primary_key(cls):
+        errors = []
+        if sum(1 for f in cls._meta.local_fields if f.primary_key) > 1:
+            errors.append(
+                checks.Error(
+                    "Model can not contain more than one 'primary_key' field.",
+                    obj=cls,
+                    id='models.E026',
+                )
+            )
+        return errors
+
     @classmethod
     def _check_index_together(cls):
         """Check the value of "index_together" option."""
diff --git a/docs/ref/checks.txt b/docs/ref/checks.txt
index 1b9fa18328..9690b5a99b 100644
--- a/docs/ref/checks.txt
+++ b/docs/ref/checks.txt
@@ -295,6 +295,7 @@ Models
   as it collides with the query lookup syntax.
 * **models.E025**: The property ``<property name>`` clashes with a related
   field accessor.
+* **models.E026**: Model can not contain more than one ``primary_key`` field.
 
 Security
 --------
diff --git a/tests/invalid_models_tests/test_models.py b/tests/invalid_models_tests/test_models.py
index cfd1a7c465..2066d4ebae 100644
--- a/tests/invalid_models_tests/test_models.py
+++ b/tests/invalid_models_tests/test_models.py
@@ -717,6 +717,19 @@ class OtherModelTests(SimpleTestCase):
             )
         ])
 
+    def test_single_primary_key(self):
+        class Model(models.Model):
+            foo = models.IntegerField(primary_key=True)
+            bar = models.IntegerField(primary_key=True)
+
+        self.assertEqual(Model.check(), [
+            Error(
+                "Model can not contain more than one 'primary_key' field.",
+                obj=Model,
+                id='models.E026',
+            )
+        ])
+
     @override_settings(TEST_SWAPPED_MODEL_BAD_VALUE='not-a-model')
     def test_swappable_missing_app_name(self):
         class Model(models.Model):