no cyclic reference possible

equipment/models.py

@@ -30,6 +30,20 @@ class EquipmentCategory(models.Model):
     def __str__(self):
         return self.name
 
+    def save(self, *args, **kwargs):
+        if self.pk:
+            done = False
+            current = self
+            while not done:
+                if current.parent == self:
+                    self.parent = None
+                    done = True
+                elif current.parent == None:
+                    done = True
+                current = current.parent
+        return super().save(*args, **kwargs)
+
+
 
 class Equipment(EventSpecificMixin, models.Model):
     name = models.CharField(