admins增加实践课程

app/models/subject.rb

@@ -7,6 +7,7 @@ class Subject < ApplicationRecord
   #status :0 编辑中  1 审核中  2 发布
   belongs_to :repertoire
   belongs_to :user
+  belongs_to :subject_level_system, optional: true
 
   has_many :stages, -> { order("stages.position ASC") }, dependent: :destroy
 

app/models/subject_level_system.rb

@@ -0,0 +1,5 @@
+class SubjectLevelSystem < ApplicationRecord
+  default_scope { order(level: :asc) }
+
+  has_many :subjects, dependent: :nullify
+end