*_path(相対パス), *_url(絶対パス)

# somewhere in view
<% debugger %> 
(rdb:25) irb
>> link_to "Diary", diaries_path
=> "Diary"
>> link_to "Diary", diaries_url
=> "Diary"

*_pathばっかり使ってて、*_urlを忘れてた！