From b8d49e77cc625c35bd6b77a33cf9ab3ab0f034c1 Mon Sep 17 00:00:00 2001
From: connorhaugh <49422820+connorhaugh@users.noreply.github.com>
Date: Wed, 3 Nov 2021 13:03:49 -0400
Subject: [PATCH] Revert "feat: Add a data migration to copy all course index
 data into MySQL"

This reverts commit 43bc683d80c620d9752e68a317d51891a00a060a.
---
 .../migrations/0002_data_migration.py         | 61 -------------------
 1 file changed, 61 deletions(-)
 delete mode 100644 common/djangoapps/split_modulestore_django/migrations/0002_data_migration.py

diff --git a/common/djangoapps/split_modulestore_django/migrations/0002_data_migration.py b/common/djangoapps/split_modulestore_django/migrations/0002_data_migration.py
deleted file mode 100644
index 3d33e53ab5..0000000000
--- a/common/djangoapps/split_modulestore_django/migrations/0002_data_migration.py
+++ /dev/null
@@ -1,61 +0,0 @@
-from django.db import migrations, models
-from django.db.utils import IntegrityError
-
-
-from xmodule.modulestore import ModuleStoreEnum
-from xmodule.modulestore.django import modulestore
-
-from ..models import SplitModulestoreCourseIndex as SplitModulestoreCourseIndex_Real
-
-
-def forwards_func(apps, schema_editor):
-    """
-    Copy all course index data from MongoDB to MySQL, unless it's already present in MySQL.
-
-    This migration is used as part of an upgrade path from storing course indexes in MongoDB to storing them in MySQL.
-    On edX.org, we began writing to MySQL+MongoDB before we deployed this migration, so some courses are already in
-    MySQL. But any courses that haven't been modified recently would only be in MongoDB and need to be copied over to
-    MySQL before we can switch reading course indexes to MySQL.
-    """
-    db_alias = schema_editor.connection.alias
-    SplitModulestoreCourseIndex = apps.get_model("split_modulestore_django", "SplitModulestoreCourseIndex")
-    split_modulestore = modulestore()._get_modulestore_by_type(ModuleStoreEnum.Type.split)
-
-    for course_index in split_modulestore.db_connection.find_matching_course_indexes(force_mongo=True):
-        data = SplitModulestoreCourseIndex_Real.fields_from_v1_schema(course_index)
-        course_id = data["course_id"]
-
-        try:
-            mysql_entry = SplitModulestoreCourseIndex.objects.get(course_id=course_id)
-            # This course index ("active version") already exists in MySQL.
-            # Let's just make sure it's the latest version. If the MongoDB somehow contains a newer version, something
-            # has gone wrong and we should investigate to ensure we're not losing any data.
-            if mysql_entry.edited_on < data["edited_on"]:
-                raise ValueError(
-                    f"Course {course_id} already exists in MySQL but the MongoDB version is newer. "
-                    "That's unexpected because since the course index table was added to MySQL, there has never been a "
-                    "time when we would write course_indexes updates only to MongoDB without also writing to MySQL."
-                )
-        except SplitModulestoreCourseIndex.DoesNotExist:
-            # This course exists in MongoDB but hasn't yet been migrated to MySQL. Do that now.
-            SplitModulestoreCourseIndex(**data).save(using=db_alias)
-
-def reverse_func(apps, schema_editor):
-    """
-    Reversing the data migration is a no-op, because edX.org used a migration path path that started with writing to
-    both MySQL+MongoDB while still reading from MongoDB, then later executed this data migration, then later cut over to
-    reading from MySQL only. If we reversed this by deleting all entries, it would undo any writes that took place
-    before this data migration, which are unrelated.
-    """
-    pass
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('split_modulestore_django', '0001_initial'),
-    ]
-
-    operations = [
-        migrations.RunPython(forwards_func, reverse_func),
-    ]