Fix N+1 queries on identity in UsersController and BoardsController (#2365)

* Fix N+1 queries on identity in UsersController and BoardsController

- Add .includes(:identity) to UsersController#index
- Add .includes(creator: :identity) to BoardsController#index
- Add N+1 regression tests for both controllers

* Simplify controller N+1 tests with query assertions

---------

Co-authored-by: Mike Dalessio <mike@37signals.com>

test/controllers/boards_controller_test.rb

@@ -278,6 +278,20 @@ class BoardsControllerTest < ActionDispatch::IntegrationTest
     assert_response :no_content
   end
 
+  test "index avoids N+1 queries on creator and identity" do
+    assert_queries_match(/FROM [`"]users[`"].* IN \(/, count: 1) do
+      assert_queries_match(/FROM [`"]identities[`"].* IN \(/, count: 1) do
+        get boards_path, as: :json
+        assert_response :success
+      end
+    end
+
+    json = @response.parsed_body
+    first_board = json.first
+    assert first_board["creator"].present?
+    assert first_board["creator"]["email_address"].present?
+  end
+
   private
     def next_page_from_link_header(link_header)
       url = link_header&.match(/<([^>]+)>;\s*rel="next"/)&.captures&.first

test/controllers/users_controller_test.rb

@@ -144,4 +144,16 @@ class UsersControllerTest < ActionDispatch::IntegrationTest
 
     assert_response :no_content
   end
+
+  test "index avoids N+1 queries on identity" do
+    sign_in_as :kevin
+
+    assert_queries_match(/FROM [`"]identities[`"].* IN \(/, count: 1) do
+      get users_path, as: :json
+      assert_response :success
+    end
+
+    json = @response.parsed_body
+    assert json.first["email_address"].present?
+  end
 end