I would love it if the Prefetch object allowed me to pass in custom
querysets when prefetching related generic foreign fields. Specifically I
want this in order to call select_related on each subgroup.
For now I've subclassed the GenericForiengKey class, overriding
get_prefetch_queryset, to allow me to use modelless querysets like this:
.prefetch_related(
Prefetch('obj', queryset=QuerySet().select_related(
"user", "poem__user", "consumer", "producer"
))
In get_prefetch_queryset, for each subgroup, I copy the select_related
options from the modelless queryset to the subgroup queryset:
qs = ct.get_all_objects_for_this_type(pk__in=fkeys)
# Copy any select related options from queryset to qs
qs = self.combine_select_related(qs, queryset)
ret_val.extend(qs)
Initially I thought I would simply be able to combine the two querysets
using QuerySet.__or__, but I noticed that Query.combine refuses to run
unless both queries are on the same model. Would there be any harm in
allowing it to combine Queries even if the qeries are not on the same
model, as long as one of the queries doesn't have a model at all? Then the
above could be changed into:
# Copy any select related options from queryset to qs
qs |= queryset
This would have the added benefit of copying other options other than
select_related.
I know this is problematic because you may not want to combine the same
queryset with each individual group. Ideally, the developer would be able
to specify a different queryset for each group kind.
.prefetch_related(
Prefetch('obj', queryset=QuerySet().select_related(
"user", "poem__user", "consumer", "producer"
))
Does anyone have any thoughts on this?
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