如果没有关注的人，sql会报错

app/controllers/users_controller.rb

@@ -949,7 +949,7 @@ class UsersController < ApplicationController
         when "current_user"
           @user_activities = UserActivity.where("user_id = #{@user.id} and ((container_type = 'Project' and container_id in #{user_project_ids} and act_type in #{project_types}) or (container_type = 'Course' and container_id in #{user_course_ids} and act_type in #{course_types}))").order('updated_at desc').limit(10).offset(@page * 10)
         else
-          blog_ids = "("+@user.blog.id.to_s+","+User.watched_by(@user.id).map{|u| u.blog.id}.join(',')+")"
+          blog_ids = "("+@user.blog.id.to_s+","+((User.watched_by(@user.id).count == 0 )? '0' :User.watched_by(@user.id).map{|u| u.blog.id}.join(','))+")"
           @user_activities = UserActivity.where("(container_type = 'Project' and container_id in #{user_project_ids} and act_type in #{project_types})" +
                                                    "or (container_type = 'Course' and container_id in #{user_course_ids} and act_type in #{course_types}) "+
                                                     "or (container_type = 'Principal' and act_type= '#{principal_types}' and container_id = #{@user.id}) " +
@@ -957,7 +957,7 @@ class UsersController < ApplicationController
       end
     else
     #  @user_activities = UserActivity.where("(container_type = 'Project' and container_id in #{user_project_ids} and act_type in #{project_types}) or (container_type = 'Course' and container_id in #{user_course_ids} and act_type in #{course_types})or (container_type = 'Principal' and act_type= '#{principal_types}' and container_id = #{@user.id})").order('updated_at desc').limit(10).offset(@page * 10)
-      blog_ids = "("+@user.blog.id.to_s+","+User.watched_by(@user.id).map{|u| u.blog.id}.join(',')+")"
+      blog_ids = "("+@user.blog.id.to_s+","+((User.watched_by(@user.id).count == 0 )? '0' :User.watched_by(@user.id).map{|u| u.blog.id}.join(','))+")"
       @user_activities = UserActivity.where("(container_type = 'Project' and container_id in #{user_project_ids} and act_type in #{project_types})" +
                                                 "or (container_type = 'Course' and container_id in #{user_course_ids} and act_type in #{course_types}) "+
                                                 "or (container_type = 'Principal' and act_type= '#{principal_types}' and container_id = #{@user.id}) " +