diff --git a/app/models/challenge.rb b/app/models/challenge.rb
index f25ce330a..9bfb89b4b 100644
--- a/app/models/challenge.rb
+++ b/app/models/challenge.rb
@@ -97,12 +97,12 @@ class Challenge < ApplicationRecord
 
   # 关卡用户通关数
   def user_passed_count
-    games.select{|game| game.status == 2}.size
+    games.where(status: 2).count
   end
 
   # 关卡用户正在挑战的人数
   def playing_count
-    games.select{|game| game.status == 0 || game.status == 1}.size
+    games.where(status: [0, 1]).count
   end
 
   def last_challenge
diff --git a/app/views/exercises/_user_exercise_info.json.jbuilder b/app/views/exercises/_user_exercise_info.json.jbuilder
index 5b5d0c725..cc10f5bb7 100644
--- a/app/views/exercises/_user_exercise_info.json.jbuilder
+++ b/app/views/exercises/_user_exercise_info.json.jbuilder
@@ -54,7 +54,7 @@ json.exercise_questions do
       this_ques_status = all_question_status.detect {|f| f[:q_id] == q.id}
       json.answer_status this_ques_status[:stand_status]
     end
-    json.user_score user_ques_answers[:user_score].to_s
+    json.user_score user_ques_answers[:user_score].present? ? user_ques_answers[:user_score].to_s : nil
     json.partial! "exercise_questions/exercise_questions",
                   question: q,
                   ex_answerer: ex_answerer,
diff --git a/lib/tasks/homework_evaluation.rake b/lib/tasks/homework_evaluation.rake
index d1fad8f14..56c46179c 100644
--- a/lib/tasks/homework_evaluation.rake
+++ b/lib/tasks/homework_evaluation.rake
@@ -24,7 +24,7 @@ namespace :homework_evaluation do
             student_works = homework_common.student_works.has_committed
           end
 
-          if student_works.size >= 2
+          if student_works.present? && student_works.length >= 2
             HomeworkEvaluationCommentAssginJob.perform_later(homework_common.id)
 
             homework_detail_manual.update_column('comment_status', 3)