old_contents: from django.db import models
  from django.contrib.contenttypes.models import ContentType
  from django.utils.encoding import force_unicode
  
  class LinksManager(models.Manager):
  
      def for_model(self, model):
          """
          QuerySet for all links for a particular model (either an instance or
          a class).
          """
          ct = ContentType.objects.get_for_model(model)
          qs = self.get_query_set().filter(active=True, content_type=ct)
          if isinstance(model, models.Model):
              qs = qs.filter(object_pk=force_unicode(model._get_pk_val()))
          return qs
  
new_contents: from django.db import models
  from django.contrib.contenttypes.models import ContentType
  from django.utils.encoding import force_unicode
  
  
  class LinksManager(models.Manager):
  
      def for_model(self, model):
          """
          QuerySet for all links for a particular model (either an instance or
          a class).
          """
          ct = ContentType.objects.get_for_model(model)
          qs = self.get_query_set().select_related('link_type').filter(
              active=True, content_type=ct)
          if isinstance(model, models.Model):
              qs = qs.filter(object_pk=force_unicode(model._get_pk_val()))
          return qs
  
subject: Use select related for link_type