python - Django预取相关和选择相关

Question

我想知道 prefetch_lated() 和 select_lated() 的行为。如果我执行类似 Model.objects.filter(...).prefetch_lated() 的操作，我会注意到发生的数据库查询要少得多。所以我最初的猜测是，如果没有在 prefetch_lated() 中指定所需的查找，它将自动遍历所有模型字段并完成所需的工作。然而，我在网上找不到任何关于它的引用，这对我来说似乎很奇怪。我的猜测是正确的还是我遗漏了什么？

Answer 1

来自the FineManual(tm) (重点是我的):

There may be some situations where you wish to call select_related() with a lot of related objects, or where you don’t know all of the relations. In these cases it is possible to call select_related() with no arguments. This will follow all non-null foreign keys it can find - nullable foreign keys must be specified. This is not recommended in most cases as it is likely to make the underlying query more complex, and return more data, than is actually needed.