This is not a great cache key. This will be `@post.to_s + : + @post.object_id` which will look something like `#<Post@1234531>:1234531`. I don't think that's really what you want. Also `@post` is not defined here...so...there's that.

I would push this code to the Post class as a class method and probably make the cache key "all_posts" or something.