Rails 5.2 关系生成两个查询的缓存键

Question

我有一个使用片段缓存的视图 ActiveRecord 关系，例如

<% cache MyModel.all do %>
...
<% end %>

我看到在这种情况下生成了两个数据库查询

SELECT COUNT(*) AS "size", MAX("my_model"."updated_at") AS timestamp FROM "my_model"
SELECT "my_model".* from "my_model"

我期待第一个，它通常是一个更有效的查询。没想到第二个。

如果我改为使用：

<% cache ActiveSupport::Cache.expand_cache_key(MyModel.all) do %>
...
<% end %>

然后我只得到具有相同结果缓存键的第一个查询。

是bug还是我做错了什么？

编辑：缩小到发生这种情况的地方：参见https://github.com/rails/rails/pull/29092#issuecomment-437572543

when normalize_version is executed, the relation does not respond to cache_version, and therefore ends up being expanded with to_a. So essentially, calling Product.all.to_a and then for each object calling cache_version, which returns nil.

Answer 1

是的，这看起来确实像一个错误。希望这会是 fixed on this PR, since my own PR for a stopgap fix was rejected

Rails 5.2 关系生成两个查询的缓存键

Rails 5.2 cache key for relations generating two queries

activerecord

caching

ruby-on-rails

activesupport