populate root_account on new DeveloperKey

refs PLAT-5518
flag=none

test plan:
* specs
* if you want, create a new DeveloperKey, set an account on it, and
note its root_account - it shouldn't be nil, and should match
the account's root account

Change-Id: I31810980aa6d6c234eb4ba0cfa3dcc21012ed250
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/234174
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Mysti Lilla <mysti@instructure.com>
QA-Review: Mysti Lilla <mysti@instructure.com>
Product-Review: Mysti Lilla <mysti@instructure.com>

app/models/account.rb

@@ -491,6 +491,10 @@ class Account < ActiveRecord::Base
     super
   end
 
+  def resolved_root_account_id
+    root_account_id || id
+  end
+
   def sub_accounts_as_options(indent = 0, preloaded_accounts = nil)
     unless preloaded_accounts
       preloaded_accounts = {}

app/models/developer_key.rb

@@ -24,6 +24,7 @@ class DeveloperKey < ActiveRecord::Base
 
   belongs_to :user
   belongs_to :account
+  belongs_to :root_account, class_name: 'Account'
 
   has_many :page_views
   has_many :access_tokens, -> { where(:workflow_state => "active") }
@@ -42,6 +43,7 @@ class DeveloperKey < ActiveRecord::Base
   before_save :nullify_empty_icon_url
   before_save :protect_default_key
   before_save :set_require_scopes
+  before_save :set_root_account
   after_save :clear_cache
   after_update :invalidate_access_tokens_if_scopes_removed!
   after_update :destroy_external_tools!, if: :destroy_external_tools?
@@ -209,6 +211,10 @@ class DeveloperKey < ActiveRecord::Base
     MultiCache.delete("developer_keys/#{vendor_code}") if vendor_code.present?
   end
 
+  def set_root_account
+    self.root_account_id ||= account&.resolved_root_account_id
+  end
+
   def authorized_for_account?(target_account)
     return false unless binding_on_in_account?(target_account)
     return true if account_id.blank?

spec/models/developer_key_spec.rb

@@ -647,6 +647,37 @@ describe DeveloperKey do
         end
       end
     end
+
+    describe 'after_save' do
+      describe 'set_root_account' do
+        context 'when account is not root account' do
+          let(:account) {
+            a = account_model
+            a.root_account = Account.create!
+            a.save!
+            a
+          }
+
+          it 'sets root account equal to account\'s root account' do
+            expect(developer_key_not_saved.root_account).to be_nil
+            developer_key_not_saved.account = account
+            developer_key_not_saved.save!
+            expect(developer_key_not_saved.root_account).to eq account.root_account
+          end
+        end
+
+        context 'when account is root account' do
+          let(:account) { account_model }
+
+          it 'set root account equal to account' do
+            expect(developer_key_not_saved.root_account).to be_nil
+            developer_key_not_saved.account = account
+            developer_key_not_saved.save!
+            expect(developer_key_not_saved.root_account).to eq account
+          end
+        end
+      end
+    end
   end
 
   describe 'associations' do