util.clj

(defn entity->map [convert-data entity]
  (reduce (fn [m attr]
            (if (keyword? attr)
              (if-let [v (attr entity)]
                (assoc m attr v)
                m)
              (let [[attr conv-fn] attr]
                (if-let [v (attr entity)]
                  (assoc m attr (conv-fn v))
                  m))))
          {}
          convert-data))

;; example
(def book-convert-data
  [:book/title
   :book/created_at
   [:book/created_by :author/id]
   [:book/comments (fn [comments] (map :comment/text comments))]])

(entity->map book-convert-data a-book-entity)
; => {:book/title "a book"
;     :book/created_at 1360418787603
;     :book/created_by "john"
;     :book/comments ("good!", "bad!")}