fix migration

fet2020/tasks/migrations/0002_slug.py

@@ -10,11 +10,16 @@ from django.utils.text import slugify
 
 def forwards_func(apps, schema_editor):
     Tasks = apps.get_model("tasks", "Task")
-    Tasks.objects.all().update(shortterm=slugify(F('name'))[1:26])
-    Tasks.objects.all().update(slug=slugify(F('shortterm')))
+    for elem in Tasks.objects.all():
+        elem.shortterm = slugify(elem.title[:25])
+        elem.slug = slugify(elem.shortterm)
+        elem.save()
 
     TaskLists = apps.get_model("tasks", "TaskList")
-    TaskLists.objects.all().update(slug=slugify(F('shortterm')))
+    for elem in TaskLists.objects.all():
+        elem.shortterm = slugify(elem.name)
+        elem.slug = slugify(elem.shortterm)
+        elem.save()
 
 
 class Migration(migrations.Migration):