Django: storing multiple Prefetch () objects in a variable or method
The documentation shows how to store the Prefetch () object in a variable:
>>> prefetch = Prefetch('choice_set', queryset=voted_choices, to_attr='voted_choices')
>>> Question.objects.prefetch_related(prefetch).get().voted_choices
[<Choice: The sky>]
However, prefetch_related accepts many Prefetch () objects, separated by commas:
>>> Question.objects.prefetch_related(Prefetch('choice_set'), Prefetch('foo')).get().voted_choices
How can this Prefetch () sequence be stored in a variable, or even better in a method for reuse?
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1 answer
I prefer to add these Prefetch related clauses to a custom QuerySet and then access the generated lists through the model properties if they exist.
using: Post.objects.filter(...).prefetch_comments()...
class PostQuerySet(models.QuerySet):
def prefetch_comments(self):
inner_qs = Comment.objects.order_by('-date')
return self.prefetch_related(Prefetch("comments", queryset=inner_qs, to_attr="comments_list"))
class Post(models.Model):
....
objects = PostQuerySet.as_manager()
@property
def most_recent_comment(self):
if hasattr(self, 'comments_list') and len(self.comments_list) > 0:
return self.comments_list[0]
return None
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