There isn't a built-in way to do this. But I've posted a technique for simulating select_related on generic relations on my blog.
Blog content summarized:
We can use Django's _content_object_cache field to essentially create our own select_related for generic relations.
generics = {}
for item in queryset:
generics.setdefault(item.content_type_id, set()).add(item.object_id)
content_types = ContentType.objects.in_bulk(generics.keys())
relations = {}
for ct, fk_list in generics.items():
ct_model = content_types[ct].model_class()
relations[ct] = ct_model.objects.in_bulk(list(fk_list))
for item in queryset:
setattr(item, '_content_object_cache',
relations[item.content_type_id][item.object_id])
Here we get all the different content types used by the relationships
in the queryset, and the set of distinct object IDs for each one, then
use the built-in in_bulk manager method to get all the content types
at once in a nice ready-to-use dictionary keyed by ID. Then, we do one
query per content type, again using in_bulk, to get all the actual
object.
Finally, we simply set the relevant object to the
_content_object_cache field of the source item. The reason we do this is that this is the attribute that Django would check, and populate if
necessary, if you called x.content_object directly. By pre-populating
it, we're ensuring that Django will never need to call the individual
lookup - in effect what we're doing is implementing a kind of
select_related() for generic relations.
