polymorphic finder

gistfile1.clj

(require '[clojure.set :as set])
(require '[clojure.java.jdbc :as j])

(def mysql-db {:subprotocol "mysql"
               :subname "//127.0.0.1:3306/clojure_test"
               :user "clojure_test"
               :password "clojure_test"})

(defn product-service [key]
  (println (str "Finding product with key: " key))
  (j/query mysql-db ["select * from product where id = ?" key]))

(defn individual-plan-service [key]
  (println (str "Finding individual plan with key: " key))
  (j/query mysql-db ["select * from individual_plan where id = ?" key]))

(defn team-plan-service [key]
  (println (str "Finding team plan with key: " key))
  (j/query mysql-db ["select * from team_plan where id = ?" key]))

(defn section-service [key]
  (println (str "Finding section with key: " key))
  (j/query mysql-db ["select * from section where id = ?" key]))

(defn not-found []
  (println "Nothing to dispatch")

;; define dispatch map
(def dispatch-map {#{:product-id :screencast-id :book-id :show-id} product-service
                   #{:individual-plan-id} individual-plan-service
                   #{:team-plan-id} team-plan-service
                   #{:section-id} section-service})

(defn- get-dispatch-entry [params dispatch-map]
  (first (filter (fn [[k v]] (seq (set/intersection k params))) dispatch-map)))

(defn requested-purchaseable
  "Takes dispatch map, set of params from request and no-arg function to be called 
   when no dispatch value is found" 
  [dispatch-map params not-found-fn]
  (let [params-keys (set (keys params))]
    (if-let [[dispatch-params service-fn] (get-dispatch-entry params-keys dispatch-map)]
      (service-fn (get params (first (set/intersection dispatch-params params-keys))))
      (not-found-fn))))

;; test various dispatches
(requested-purchaseable dispatch-map {:product-id 10} not-found)

(requested-purchaseable dispatch-map {:book-id 11} not-found)

(requested-purchaseable dispatch-map {:individual-plan-id 12} not-found)

(requested-purchaseable dispatch-map {:team-plan-id 13} not-found)

(requested-purchaseable dispatch-map {:section-id 14} not-found)