add root_account_id to account_users

closes PLAT-5579

test plan:
* verify migrations run
* verify root_account_id can be set on an AccountUser
* verify AccountUser_s live on the same shard as their root account

Change-Id: I5a227a9d62552803085eb2db6d6568f58020d0d0
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/235721
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Product-Review: Xander Moffatt <xmoffatt@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Reviewed-by: Clint Furse <cfurse@instructure.com>
QA-Review: Clint Furse <cfurse@instructure.com>

app/models/account.rb

@@ -1099,7 +1099,7 @@ class Account < ActiveRecord::Base
     raise "must be a root account" unless self.root_account?
     Shard.partition_by_shard(account_chain(include_site_admin: true).uniq) do |accounts|
       next unless user.associated_shards.include?(Shard.current)
-      AccountUser.active.eager_load(:account).where("user_id=? AND (root_account_id IN (?) OR account_id IN (?))", user, accounts, accounts)
+      AccountUser.active.eager_load(:account).where("user_id=? AND (accounts.root_account_id IN (?) OR account_id IN (?))", user, accounts, accounts)
     end
   end
 

db/migrate/20200429215549_add_root_account_id_to_account_users.rb

@@ -0,0 +1,32 @@
+#
+# 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 AddRootAccountIdToAccountUsers < ActiveRecord::Migration[5.2]
+  include MigrationHelpers::AddColumnAndFk
+
+  tag :predeploy
+  disable_ddl_transaction!
+
+  def up
+    add_column_and_fk :account_users, :root_account_id, :accounts
+    add_index :account_users, :root_account_id, algorithm: :concurrently
+  end
+
+  def down
+    remove_column :account_users, :root_account_id
+  end
+end