0113 Migration Fix: Make github_branch migration idempotent: add column only if not exists (#4754)

Author: RishabhJain2018

apps/challenges/migrations/0113_add_github_branch_field_and_unique_constraint.py

@@ -1,20 +1,6 @@
 # Generated by Django 2.2.20 on 2025-07-09 15:00
 
-from django.db import migrations, models
-
-
-def fix_duplicate_github_fields(apps, schema_editor):
-    """
-    No data migration needed since we're using a partial unique constraint.
-    """
-    pass
-
-
-def reverse_fix_duplicate_github_fields(apps, schema_editor):
-    """
-    No reverse migration needed.
-    """
-    pass
+from django.db import migrations
 
 
 class Migration(migrations.Migration):
@@ -24,20 +10,36 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.AddField(
-            model_name="challenge",
-            name="github_branch",
-            field=models.CharField(
-                blank=True, default="", max_length=200, null=True
+        migrations.RunSQL(
+            sql=(
+                "DO $$\n"
+                "BEGIN\n"
+                "    IF NOT EXISTS (\n"
+                "        SELECT 1 FROM information_schema.columns\n"
+                "        WHERE table_name='challenge'\n"
+                "        AND column_name='github_branch'\n"
+                "    ) THEN\n"
+                "        ALTER TABLE challenge ADD COLUMN github_branch "
+                "varchar(200) NULL DEFAULT '';\n"
+                "    END IF;\n"
+                "END$$;"
+            ),
+            reverse_sql=(
+                "ALTER TABLE challenge DROP COLUMN IF EXISTS github_branch;"
             ),
         ),
-        migrations.RunPython(
-            fix_duplicate_github_fields,
-            reverse_fix_duplicate_github_fields,
-        ),
-        # Add a partial unique constraint that only applies when both fields are not empty
+        # Add a partial unique constraint
+        # Only applies when both fields are not empty
         migrations.RunSQL(
-            "CREATE UNIQUE INDEX challenge_github_repo_branch_partial_idx ON challenge (github_repository, github_branch) WHERE github_repository != '' AND github_branch != '';",
-            reverse_sql="DROP INDEX IF EXISTS challenge_github_repo_branch_partial_idx;",
+            (
+                "CREATE UNIQUE INDEX challenge_github_repo_branch_partial_idx "
+                "ON challenge (github_repository, github_branch) "
+                "WHERE github_repository != '' "
+                "AND github_branch != '';"
+            ),
+            reverse_sql=(
+                "DROP INDEX IF EXISTS "
+                "challenge_github_repo_branch_partial_idx;"
+            ),
         ),
     ]