From 1b3a949ba26ca8fefde7fa224e11c4aadbbdd724 Mon Sep 17 00:00:00 2001
From: Mariusz Felisiak <felisiak.mariusz@gmail.com>
Date: Fri, 29 Apr 2022 21:43:55 +0200
Subject: [PATCH] Refs #33671 -- Fixed migrations crash when adding collation
 to a primary key on Oracle.

---
 django/db/backends/oracle/schema.py |  8 ++++++++
 tests/schema/tests.py               | 25 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/django/db/backends/oracle/schema.py b/django/db/backends/oracle/schema.py
index d6b04fe9a1..f2a5099110 100644
--- a/django/db/backends/oracle/schema.py
+++ b/django/db/backends/oracle/schema.py
@@ -91,6 +91,14 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             elif "ORA-30673" in description and old_field.primary_key:
                 self._delete_primary_key(model, strict=True)
                 self._alter_field_type_workaround(model, old_field, new_field)
+            # If a collation is changing on a primary key, drop the primary key
+            # first.
+            elif "ORA-43923" in description and old_field.primary_key:
+                self._delete_primary_key(model, strict=True)
+                self.alter_field(model, old_field, new_field, strict)
+                # Restore a primary key, if needed.
+                if new_field.primary_key:
+                    self.execute(self._create_primary_key_sql(model, new_field))
             else:
                 raise
 
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 3fe41f5336..2d12796cbd 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -4608,6 +4608,31 @@ class SchemaTests(TransactionTestCase):
             editor.alter_field(Author, new_field, old_field, strict=True)
         self.assertIsNone(self.get_column_collation(Author._meta.db_table, "name"))
 
+    @skipUnlessDBFeature("supports_collation_on_charfield")
+    def test_alter_primary_key_db_collation(self):
+        collation = connection.features.test_collations.get("non_default")
+        if not collation:
+            self.skipTest("Language collations are not supported.")
+
+        with connection.schema_editor() as editor:
+            editor.create_model(Thing)
+
+        old_field = Thing._meta.get_field("when")
+        new_field = CharField(max_length=1, db_collation=collation, primary_key=True)
+        new_field.set_attributes_from_name("when")
+        new_field.model = Thing
+        with connection.schema_editor() as editor:
+            editor.alter_field(Thing, old_field, new_field, strict=True)
+        self.assertEqual(self.get_primary_key(Thing._meta.db_table), "when")
+        self.assertEqual(
+            self.get_column_collation(Thing._meta.db_table, "when"),
+            collation,
+        )
+        with connection.schema_editor() as editor:
+            editor.alter_field(Thing, new_field, old_field, strict=True)
+        self.assertEqual(self.get_primary_key(Thing._meta.db_table), "when")
+        self.assertIsNone(self.get_column_collation(Thing._meta.db_table, "when"))
+
     @skipUnlessDBFeature(
         "supports_collation_on_charfield", "supports_collation_on_textfield"
     )