Display in admin and export 'ext_id' field

stages/admin.py

@@ -20,7 +20,8 @@ class StudentAdmin(admin.ModelAdmin):
     list_filter = ('klass', 'archived')
     search_fields = ('last_name', 'first_name', 'pcode', 'city', 'klass__name')
     fields = (('last_name', 'first_name'), 'street', ('pcode', 'city'), 'email',
-              ('tel', 'mobile'), 'birth_date', 'klass', 'archived')
+              ('tel', 'mobile'), ('birth_date', 'ext_id'), 'klass', 'archived')
+    readonly_fields = ('ext_id',)
     actions = ['archive']
 
     def archive(self, request, queryset):

stages/views.py

@@ -205,6 +205,7 @@ def del_training(request):
 
 EXPORT_FIELDS = [
     ('Prénom', 'student__first_name'), ('Nom', 'student__last_name'),
+    ('ID externe', 'student__ext_id'),
     ('Classe', 'student__klass__name'), ('Filière', 'student__klass__section__name'),
     ('Nom du stage', 'availability__period__title'),
     ('Début', 'availability__period__start_date'), ('Fin', 'availability__period__end_date'),