old_contents: from django.contrib import admin
  
  from .forms import BaseForm
  from .models import (
      Concept,
      ConceptGraph,
      Lesson,
      ConceptLink,
      UnitLesson,
      Unit,
      Response,
      StudentError,
      Course,
      CourseUnit,
      Role
  )
  
  
  MODELS = (
      Concept,
      ConceptGraph,
      Lesson,
      ConceptLink,
      UnitLesson,
      Unit,
      Response,
      StudentError,
      Course,
      CourseUnit
  )
  
  
  class BaseAdmin(admin.ModelAdmin):
      """
      Base class for admin models.
      """
      def get_form(self, request, obj=None, **kwargs):
          form = super(BaseAdmin, self).get_form(request, obj, **kwargs)
          form.current_user = request.user
          return form
  
      form = BaseForm
  
  
  @admin.register(*MODELS)
  class AdminModel(BaseAdmin):
      pass
  
  
  @admin.register(Role)
  class AdminRole(admin.ModelAdmin):
      list_display = ('role', 'course', 'user')
  
new_contents: from django.contrib import admin
  
  from .forms import BaseForm
  from .models import (
      Concept,
      ConceptGraph,
      Lesson,
      ConceptLink,
      UnitLesson,
      Unit,
      Response,
      StudentError,
      Course,
      CourseUnit,
      Role
  )
  
  
  MODELS = (
      Concept,
      ConceptGraph,
      Lesson,
      ConceptLink,
      UnitLesson,
      Unit,
      Course,
      CourseUnit
  )
  
  
  class BaseAdmin(admin.ModelAdmin):
      """
      Base class for admin models.
      """
      def get_form(self, request, obj=None, **kwargs):
          form = super(BaseAdmin, self).get_form(request, obj, **kwargs)
          form.current_user = request.user
          return form
  
      form = BaseForm
  
  
  @admin.register(*MODELS)
  class AdminModel(BaseAdmin):
      pass
  
  
  @admin.register(Role)
  class AdminRole(admin.ModelAdmin):
      list_display = ('role', 'course', 'user')
  
  
  @admin.register(Response)
  class AdminResponse(admin.ModelAdmin):
      raw_id_fields = ('lesson', 'unitLesson')
  
  
  @admin.register(StudentError)
  class AdminStudentError(admin.ModelAdmin):
      raw_id_fields = ('response', 'errorModel')
  
subject: fix issue#195 - nginx 504 error