Python 防止使用多对多字段进行双重查询

在我的模型中，我得到了：

Model(models.Model):
  prices = models.ManyToManyField('Price')

  def foo(self):
    obj_prices = self.prices.all() # I expect save all prices in 'obj_prices'

    fist_price = obj_prices[0]     # I need the first price

    for obj_price in obj_prices:   # Also I need to check each price
      // Do something

SELECT ••• FROM `app_model` ASC LIMIT 1

SELECT ••• FROM `app_model` ASC

正如我所评论的，我希望将所有价格保存在“obj_prices”中，以防止多次查询。但我用调试工具栏检查了一下，得到了：

Model(models.Model):
  prices = models.ManyToManyField('Price')

  def foo(self):
    obj_prices = self.prices.all() # I expect save all prices in 'obj_prices'

    fist_price = obj_prices[0]     # I need the first price

    for obj_price in obj_prices:   # Also I need to check each price
      // Do something

SELECT ••• FROM `app_model` ASC LIMIT 1

SELECT ••• FROM `app_model` ASC

---

有什么想法吗？谢谢。

查询集很懒惰，只在需要时执行。它试图通过在第一个查询中只执行限制1来帮你一个忙

如果要以任何方式迭代queryset，请强制执行：

obj_prices = list(self.prices.all())