crud.clj

(defprotocol CRUD
  (create [this entity])
  (get [this id])
  (save [this id updates])
  (delete [this id]))

(defn create-db []
  (let [db (ref {})]
    (reify CRUD
      (create [_ entity]
        (let [id (str (java.util.UUID/randomUUID))]
          (dosync (alter db assoc id (assoc entity :id id)))
            entity))
      (get [_ id]
        (@db id))
      (save [_ id updates]
        (dosync (alter db update-in [id] merge updates)))
      (delete [_ id]
        (dosync (dissoc db id))))))