Why is my Ring session being reset?

Question

I want different handlers to set different keys in the session without affecting each other. I'm working from this wiki article, which advises using assoc. I thought I could use assoc-in to update a path in the session.

(defn handler-one
  [request]
  (prn "Session before one" (:session request))
  (-> (response "ONE")
          (content-type "text/plain")
          (#(assoc-in % [:session :key-one] "one"))))

(defn handler-two
  [request]
  (prn "Session before two" (:session request))
  (-> (response "TWO")
          (content-type "text/plain")
          (#(assoc-in % [:session :key-two] "two"))))

If I call handler-one repeatedly it prints Session before one {:key-one "one"} and likewise handler-two prints the previous session values.

By setting a session key using assoc-in I would expect both keys to be set, i.e. {:key-one "one" :key-two "two"}. But it appears that the entire session dictionary is replaced.

Am I doing this wrong?

Answer 1

You're printing the session in request, but you're assoc'ing on the (nonexistent) session in response so you end up with a session with only the last added property. You should get the session out of request, assoc into that and then return the new session as part of the response.