diff --git a/app/helpers/lti_helper.rb b/app/helpers/lti_helper.rb
index f46974cd..433468a1 100644
--- a/app/helpers/lti_helper.rb
+++ b/app/helpers/lti_helper.rb
@@ -5,6 +5,6 @@ module LtiHelper
     lti_parameters = LtiParameter.where(consumers_id: consumer_id,
                                        external_users_id: external_user_id,
                                        exercises_id: exercise_id).lis_outcome_service_url?
-    !lti_parameters.nil? && lti_parameters.size > 0
+    !lti_parameters.nil? && lti_parameters.present?
   end
-end
\ No newline at end of file
+end
diff --git a/db/migrate/20180823135317_add_index_for_testrun_submission_id.rb b/db/migrate/20180823135317_add_index_for_testrun_submission_id.rb
new file mode 100644
index 00000000..d0511dc9
--- /dev/null
+++ b/db/migrate/20180823135317_add_index_for_testrun_submission_id.rb
@@ -0,0 +1,5 @@
+class AddIndexForTestrunSubmissionId < ActiveRecord::Migration
+  def change
+    add_index :testruns, :submission_id
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 2646f080..2e1ec3cb 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180815115351) do
+ActiveRecord::Schema.define(version: 20180823135317) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -383,6 +383,8 @@ ActiveRecord::Schema.define(version: 20180815115351) do
     t.string   "cause"
   end
 
+  add_index "testruns", ["submission_id"], name: "index_testruns_on_submission_id", using: :btree
+
   create_table "user_exercise_feedbacks", force: :cascade do |t|
     t.integer  "exercise_id",             null: false
     t.integer  "user_id",                 null: false