Update grade change tables for override grades

flag=none
closes EVAL-1065

Test plan:
- "up" migration:
  - Ensure migrations run properly
  - After the migration finishes, check that the assignment_id,
    submission_id and submission_version_number columns in the
    auditor_grade_change_records_* tables do *not* have not-null
    constraints
  - Check that the grading_period_id column exists on said tables, along
    with an accompanying foreign key
- "down" migration:
  - Check that the assignment_id, submission_id and
    submission_version_number column once again have a not-null
    constraint
  - Check that the grading_period_id column no longer exists

Change-Id: I82d0325ea88f88138e78901415ed8fbe0d7d2814
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/243691
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jacob Burroughs <jburroughs@instructure.com>
Reviewed-by: Spencer Olson <solson@instructure.com>
QA-Review: Adrian Packel <apackel@instructure.com>
Product-Review: Syed Hussain <shussain@instructure.com>

db/migrate/20200728210143_adjust_grade_change_tables_for_override_grades.partitions.rb

@@ -0,0 +1,55 @@
+#
+# Copyright (C) 2020 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+class AdjustGradeChangeTablesForOverrideGrades < CanvasPartman::Migration
+  include MigrationHelpers::AddColumnAndFk
+
+  disable_ddl_transaction!
+  tag :postdeploy
+  self.base_class = Auditors::ActiveRecord::GradeChangeRecord
+
+  GRADE_CHANGE_BASE_TABLE = :auditor_grade_change_records
+  COLUMNS = %i[assignment_id submission_id submission_version_number].freeze
+
+  def self.up
+    COLUMNS.each { |column| change_column_null(GRADE_CHANGE_BASE_TABLE, column, true) }
+
+    add_column_and_fk GRADE_CHANGE_BASE_TABLE, :grading_period_id, :grading_periods, if_not_exists: true
+
+    # The new column propagates to the partitioned tables, but the foreign key
+    # constraint does not, so add it manually
+    with_each_partition do |partition|
+      unless connection.foreign_key_exists?(partition, column: :grading_period_id)
+        foreign_key = connection.send(:foreign_key_name, partition, column: :grading_period_id)
+        execute("ALTER TABLE #{connection.quote_table_name(partition)} ADD CONSTRAINT #{foreign_key} FOREIGN KEY (grading_period_id) REFERENCES #{connection.quote_table_name('grading_periods')} (id)")
+      end
+    end
+  end
+
+  def self.down
+    remove_records_with_null_values
+
+    remove_column GRADE_CHANGE_BASE_TABLE, :grading_period_id
+    COLUMNS.each { |column| change_column_null(GRADE_CHANGE_BASE_TABLE, column, false) }
+  end
+
+  def self.remove_records_with_null_values
+    null_record_scope = base_class.where("assignment_id IS NULL OR submission_id IS NULL")
+    null_record_scope.order(created_at: :asc).find_ids_in_batches(batch_size: 10_000) do |ids|
+      base_class.where(id: ids).delete_all
+    end
+  end
+end