Select and filter related models

Question

I have the following models:

class Competition(models.Model): # ... class Result(models.Model): # ... competition = ForeignKey(Competition, on_delete=models.CASCADE, related_name='individual_results', related_query_name='individual_results') athlete = ForeignKey(Athlete, on_delete=models.CASCADE) class Athlete(models.Model): # ...

What I'd like to do is create an overview for each athlete and display the results for that athlete grouped by competition.

Tried something like this:

athlete = Athlete.objects.get(pk=1) competitions = Competition.objects .prefetch_related('individual_results') .filter(individual_results__athlete=athlete)

But when I do competition.indvidual_results.all in a template, it displays all results from the competition and not only the ones for that athlete.

willeM_ Van Onsem · Accepted Answer · 2019-08-24 11:14:26Z

A .filter(..) does not filter the related managers. It can be used to filter when you aggregate, but not items in the prefetch manager.

You can however use a Prefetch object [Django-doc], like:

results = Result.objects.filter(athlete_id=1) competitions = Competition.objects.prefetch_related( Prefetch('individual_results', queryset=results, to_attr='athlete_results') )

Now the individual results for the athlete with id=1, are stored in an attribute athlete_results in the Competitions that arise from this queryset.

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