code: def get_resource_models(cls):
          
          from django.apps import apps
  
          return {'.'.join([service['name'], attrs['name']]): apps.get_model(resource)
                  for service in cls._registry.values()
                  for resource, attrs in service['resources'].items()}
docs: Get a list of resource models.
              {
                  'DigitalOcean.Droplet': waldur_digitalocean.models.Droplet,
                  'JIRA.Project': waldur_jira.models.Project,
                  'OpenStack.Tenant': waldur_openstack.models.Tenant
              }