content: from django.db import migrations
  import mptt
  import mptt.managers
  
  
  def rebuild_mptt(apps, schema_editor):
      """
      Construct the MPTT hierarchy.
      """
      Platform = apps.get_model('dcim', 'Platform')
      manager = mptt.managers.TreeManager()
      manager.model = Platform
      mptt.register(Platform)
      manager.contribute_to_class(Platform, 'objects')
      manager.rebuild()
  
  
  class Migration(migrations.Migration):
  
      dependencies = [
          ('dcim', '0213_platform_parent'),
      ]
  
      operations = [
          migrations.RunPython(
              code=rebuild_mptt,
              reverse_code=migrations.RunPython.noop
          ),
      ]
  