设置头像url

app/views/users/_user.json.jbuilder

@@ -3,5 +3,5 @@ json.login user.login
 json.name user.full_name
 json.grade user.grade
 # json.email user.mail # 邮箱原则上不暴露的，如果实在需要的话只能对某些具体的接口公开
-json.image_url url_to_avatar(user)
+json.image_url image_url(url_to_avatar(user))
 json.school user.school_name

db/migrate/20190715073825_add_test_for_challenges.rb

@@ -0,0 +1,9 @@
+class AddTestForChallenges < ActiveRecord::Migration[5.2]
+  def change
+    challenge_answers = ChallengeAnswer.all
+    byebug
+    challenge_answers.find_each do |ca|
+      puts()
+    end
+  end
+end