如何优化以下查询集？
[link.goal for link in self.child_links.all()]
我想摆脱 for 循环并只访问数据库一次。
我有以下代码:
class Goal(models.Model):
name = models.CharField(max_length=300)
progress = models.SmallIntegerField(default=0)
def __str__(self):
return self.name
def calc_progress(self):
progress = 0
subgoals = [link.goal for link in self.child_links.all()]
for subgoal in subgoals:
progress += subgoal.weight * subgoal.progress
weight += subgoal.weight
progress = progress / weight / len(subgoals)
self.progress = int(progress)
class Link(models.Model):
parent_goal = models.ForeignKey(Goal, on_delete=models.CASCADE, related_name="child_links")
goal = models.ForeignKey(Goal, on_delete=models.CASCADE, related_name="parent_links")
weight = models.SmallIntegerField(default=1)
def __str__(self):
return str(self.parent_goal) + "-->" + str(self.goal)
最佳答案
I want to get rid of the for loop and hit the database only once.
goal 是一个 ForeignKey，所以这意味着这是一个传统的 N+1 问题，您可以减少负载，通过使用 .select_related(..) 或 .prefetch_related(..):
[link.goal for link in self.child_links<b>.select_related('goal')</b>.all()]关于python - 为循环优化 Django Queryset，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53693786/