django查询优化之是否存在

res = Booking.objects.filter()
# 方法一：exists()
if res.exists():
    print('queryset has data')
else:
    print('queryset has no data')

# 方法二：count() ==0
if res.count() == 0:
    print('empty')

# 方法三：
if res:
   print('queryset has data')
else:
    print('queryset has no data')

总之，queryset.exists() > queryset.count() > queryset

性能比是exists()最佳，而直接用queryset来判断是最差