transform ratios to map and back again

why_clojure_rawks.clj

(defmulti transform-ratio
  "Transforms Ratios to and from maps. Passes other values through without changing them unless they are of type clojure.lang.Ratio or clojure.lang.PersistenArrayMap. In the case of a map they must be annotated with :t \"ratio\" otherwise they'll get passed through too"

  class)

(defmethod transform-ratio :default [v] v)

(defmethod transform-ratio clojure.lang.Ratio [value]
  {:n (numerator value)
   :d (denominator value)
   :t "ratio"})

(defmethod transform-ratio clojure.lang.PersistentArrayMap [value]
  (if (and (contains? value :t)
           (= "ratio" (:t value)))
    
    (/ (:n value) (:d value))

    value))

;; riak helper
(defn- put [bucket key data]
  (let [bucket (name bucket)
        data (postwalk transform-ratio data)]

    (riak/put rc bucket key
              {:value (.getBytes (json/json-str data))
               :content-type "application/json"})))