old_contents: from django.contrib import admin
  from django import forms
  
  from .models import BluePrintCreator, NeedBluePrint
  
  
  class BluePrintCreatorAdminForm(forms.ModelForm):
      class Meta:
          model = BluePrintCreator
          fields = '__all__'
  
      def clean(self):
          try:
              if BluePrintCreator.objects.get(location=self.data['location']):
                  raise forms.ValidationError("Ort hat bereits eine Vorlage!")
          except Exception:
              return self.cleaned_data
  
  
  class BluePrintCreatorAdmin(admin.ModelAdmin):
      form = BluePrintCreatorAdminForm
      filter_horizontal = ('needs',)
  
      fieldsets = (
          (None, {
              'fields': ('title', 'location')
          }),
          (None, {
              'classes': ('needs_in_blueprint',),
              'fields': ('needs',)
          }),
      )
  
  
  class NeedBluePrintAdmin(admin.ModelAdmin):
      list_display = ['topic', 'get_location']
  
  
  admin.site.register(BluePrintCreator, BluePrintCreatorAdmin)
  admin.site.register(NeedBluePrint, NeedBluePrintAdmin)
  
new_contents: from django.contrib import admin
  from django import forms
  
  from .models import BluePrintCreator, NeedBluePrint
  
  
  class BluePrintCreatorAdminForm(forms.ModelForm):
      class Meta:
          model = BluePrintCreator
          fields = '__all__'
  
      def clean(self):
          try:
              if BluePrintCreator.objects.get(location=self.data['location']):
                  raise forms.ValidationError("Ort hat bereits eine Vorlage!")
          except Exception:
              return self.cleaned_data
  
  
  class BluePrintCreatorAdmin(admin.ModelAdmin):
      form = BluePrintCreatorAdminForm
      filter_horizontal = ('needs',)
  
      fieldsets = (
          (None, {
              'fields': ('title', 'location')
          }),
          (None, {
              'classes': ('needs_in_blueprint',),
              'fields': ('needs',)
          }),
      )
  
  
  class NeedBluePrintAdmin(admin.ModelAdmin):
      list_display = ['topic', 'get_location', 'from_time', 'to_time']
  
  
  admin.site.register(BluePrintCreator, BluePrintCreatorAdmin)
  admin.site.register(NeedBluePrint, NeedBluePrintAdmin)
  
subject: add dates in admin