显示 django-admin 中相关 m2o 对象的字段

Question

I have model Job which is shown using modelAdmin. And also I have stop model:

class Stop(models.Model):
    ...
    job = models.ForeignKey(to=Job, ...)
    stop_number = ...
    ...

Job can have from 2 to 3 stops.

I've tried to show first and second stop names using:

@admin.register(Job)
class JobAdmin(admin.ModelAdmin):
    def stop_1(self, obj):
        stop = self.stop_set.objects.get(stop_number=1)
        return stop.name

    def stop_2(self, obj):
        stop = self.stop_set.objects.get(stop_number=2)
        return stop.name

    list_display = ('stop_1', 'stop_2', ...)

But it does many SQL queries on each list view rendering and makes it way too slow. Is there a way to query needed info in single or just few queries?

Answer 1

You should add prefetch_related to get_queryset to prefetch the objects in one query and reduce the number of queries.

A couple more points:

• stop_set is a queryset, you can call .get() on it without objects
• You want to get stop_set off obj not self . obj , is the Job object, which will refer to a row in the list display. self is the JobAdmin class.

@admin.register(Job)
class JobAdmin(admin.ModelAdmin):
    def get_queryset(self, request):
        qs = super().get_queryset(request).prefetch_related('stop_set')
        return qs

    def stop_1(self, obj):
        stop = obj.stop_set.get(stop_number=1)
        return stop.name

    def stop_2(self, obj):
        stop = obj.stop_set.get(stop_number=2)
        return stop.name

    list_display = ('stop_1', 'stop_2', ...)