content: from django.apps import apps
  from django.contrib.contenttypes.models import ContentType
  from django.db import router, transaction
  
  
  def compile_path_node(ct_id, object_id):
      return f'{ct_id}:{object_id}'
  
  
  def decompile_path_node(repr):
      ct_id, object_id = repr.split(':')
      return int(ct_id), int(object_id)
  
  
  def object_to_path_node(obj):
      """
      Return a representation of an object suitable for inclusion in a CablePath path. Node representation is in the
      form <ContentType ID>:<Object ID>.
      """
      ct = ContentType.objects.get_for_model(obj)
      return compile_path_node(ct.pk, obj.pk)
  
  
  def path_node_to_object(repr):
      """
      Given the string representation of a path node, return the corresponding instance. If the object no longer
      exists, return None.
      """
      ct_id, object_id = decompile_path_node(repr)
      ct = ContentType.objects.get_for_id(ct_id)
      return ct.model_class().objects.filter(pk=object_id).first()
  
  
  def create_cablepath(terminations):
      """
      Create CablePaths for all paths originating from the specified set of nodes.
  
      :param terminations: Iterable of CableTermination objects
      """
      from dcim.models import CablePath
  
      cp = CablePath.from_origin(terminations)
      if cp:
          cp.save()
  
  
  def rebuild_paths(terminations):
      """
      Rebuild all CablePaths which traverse the specified nodes.
      """
      from dcim.models import CablePath
  
      for obj in terminations:
          cable_paths = CablePath.objects.filter(_nodes__contains=obj)
  
          with transaction.atomic(using=router.db_for_write(CablePath)):
              for cp in cable_paths:
                  cp.delete()
                  create_cablepath(cp.origins)
  
  
  def update_interface_bridges(device, interface_templates, module=None):
      """
      Used for device and module instantiation. Iterates all InterfaceTemplates with a bridge assigned
      and applies it to the actual interfaces.
      """
      Interface = apps.get_model('dcim', 'Interface')
  
      for interface_template in interface_templates.exclude(bridge=None):
          interface = Interface.objects.get(device=device, name=interface_template.resolve_name(module=module))
  
          if interface_template.bridge:
              interface.bridge = Interface.objects.get(
                  device=device,
                  name=interface_template.bridge.resolve_name(module=module)
              )
              interface.full_clean()
              interface.save()
  