fix: make migration 0013 reversible (#533)

* fix: make migration 0013 reversible

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix: write backwards data migration function

* fix: only call json.dumps if fields are TextField

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

social_django/migrations/0013_migrate_extra_data.py

@@ -2,7 +2,7 @@
 
 import json
 
-from django.db import migrations
+from django.db import migrations, models
 
 
 def migrate_json_field(apps, schema_editor):
@@ -41,11 +41,50 @@ def migrate_json_field(apps, schema_editor):
         auth.save(update_fields=["data_new"])
 
 
+def migrate_json_field_backwards(apps, schema_editor):
+    UserSocialAuth = apps.get_model("social_django", "UserSocialAuth")
+    Partial = apps.get_model("social_django", "Partial")
+    db_alias = schema_editor.connection.alias
+    to_be_updated = []
+
+    is_text_field = isinstance(
+        UserSocialAuth._meta.get_field("extra_data"),
+        models.TextField,
+    )
+    for auth in UserSocialAuth.objects.using(db_alias).iterator():
+        new_value = auth.extra_data_new
+        if is_text_field:
+            new_value = json.dumps(new_value)
+        auth.extra_data = new_value
+        to_be_updated.append(auth)
+
+        if len(to_be_updated) >= 1000:
+            UserSocialAuth.objects.bulk_update(to_be_updated, ["extra_data"])
+            to_be_updated.clear()
+
+    if to_be_updated:
+        UserSocialAuth.objects.bulk_update(to_be_updated, ["extra_data"])
+        to_be_updated.clear()
+
+    is_text_field = issubclass(
+        Partial._meta.get_field("data"),
+        models.TextField,
+    )
+    for auth in Partial.objects.using(db_alias).all():
+        new_value = auth.data_new
+        if is_text_field:
+            new_value = json.dumps(new_value)
+        auth.data = new_value
+        auth.save(update_fields=["data"])
+
+
 class Migration(migrations.Migration):
     dependencies = [
         ("social_django", "0012_usersocialauth_extra_data_new"),
     ]
 
     operations = [
-        migrations.RunPython(migrate_json_field, elidable=True),
+        migrations.RunPython(
+            migrate_json_field, migrate_json_field_backwards, elidable=True
+        ),
     ]