>>> a = Product.objects.select_related('main_category','sub_category','nutrient').get(id=1)
>>> a.main_category.name
'음료'
c = Product.objects.prefetch_related('allergen').get(id=1)
c.allergen.all()
d = [{ 'id':i.id ,'name':i.name } for i in c.allergen.all()]