fix: Convert UUIDField columns to uuid type for MariaDB (#37494)

The behavior of the MariaDB backend has changed behavior for UUIDField
from a `CharField(32)` to an actual `uuid` type. This is not converted
automatically, which results in all writes to the affected columns to
error with a message about the data being too long. This is because the
actual tring being written is a UUID with the `-` included, resulting in
a 36 character value which can't be inserted into a 32 character column.

openedx/core/djangoapps/external_user_ids/migrations/0009_mariadb_uuid_conversion.py

@@ -0,0 +1,86 @@
+# Generated migration for MariaDB UUID field conversion (Django 5.2)
+"""
+Migration to convert UUIDField from char(32) to uuid type for MariaDB compatibility.
+
+This migration is necessary because Django 5 changed the behavior of UUIDField for MariaDB
+databases from using CharField(32) to using a proper UUID type. This change isn't managed
+automatically, so we need to generate migrations to safely convert the columns.
+
+This migration only executes for MariaDB databases and is a no-op for other backends.
+
+See: https://www.albertyw.com/note/django-5-mariadb-uuidfield
+"""
+
+from django.db import migrations
+
+
+def apply_mariadb_migration(apps, schema_editor):
+    """Apply the migration only for MariaDB databases."""
+    connection = schema_editor.connection
+    
+    # Check if this is a MariaDB database
+    if connection.vendor != 'mysql':
+        return
+    
+    # Additional check for MariaDB specifically (vs MySQL)
+    with connection.cursor() as cursor:
+        cursor.execute("SELECT VERSION()")
+        version = cursor.fetchone()[0]
+        if 'mariadb' not in version.lower():
+            return
+    
+    # Apply the field changes for MariaDB
+    with connection.cursor() as cursor:
+        # Convert external_user_id in externalid table
+        cursor.execute(
+            "ALTER TABLE external_user_ids_externalid "
+            "MODIFY external_user_id uuid NOT NULL"
+        )
+        # Convert external_user_id in historicalexternalid table
+        cursor.execute(
+            "ALTER TABLE external_user_ids_historicalexternalid "
+            "MODIFY external_user_id uuid NOT NULL"
+        )
+
+
+def reverse_mariadb_migration(apps, schema_editor):
+    """Reverse the migration only for MariaDB databases."""
+    connection = schema_editor.connection
+    
+    # Check if this is a MariaDB database
+    if connection.vendor != 'mysql':
+        return
+    
+    # Additional check for MariaDB specifically (vs MySQL)
+    with connection.cursor() as cursor:
+        cursor.execute("SELECT VERSION()")
+        version = cursor.fetchone()[0]
+        if 'mariadb' not in version.lower():
+            return
+    
+    # Reverse the field changes for MariaDB
+    with connection.cursor() as cursor:
+        # Revert external_user_id in externalid table
+        cursor.execute(
+            "ALTER TABLE external_user_ids_externalid "
+            "MODIFY external_user_id char(32) NOT NULL"
+        )
+        # Revert external_user_id in historicalexternalid table
+        cursor.execute(
+            "ALTER TABLE external_user_ids_historicalexternalid "
+            "MODIFY external_user_id char(32) NOT NULL"
+        )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('external_user_ids', '0008_remove_mbcoaching_extid_type'),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            code=apply_mariadb_migration,
+            reverse_code=reverse_mariadb_migration,
+        ),
+    ]