Radiance Interface Function for MongoDB

;; Looks nice but is shit in terms of performance.
(defmethod db-iterate ((db mongodb) (collection string) query function &key (skip 0) (limit 0) sort)
  "Iterate over a set of data. The collected return values are returned."
  (if sort (setf query (kv (kv "query" query) (kv "orderby" (alist->document sort)))))
  (let ((result (db.find collection query :limit limit :skip skip)))
    (multiple-value-bind (iterator collection docs) (cl-mongo::db.iterator result)
      (loop
         for next = '(NIL NIL) then (db.next collection iter)
         for iter = iterator then (nth-value 0 (cl-mongo::db.iterator next))
         for idoc = docs then (append (cdr idoc) (second next))
         for doc = (car idoc)
         while doc
         collect (funcall function doc)))))

;; Two loops and the performance is increased by a factor of ~30.
(defmethod db-iterate ((db mongodb) (collection string) query function &key (skip 0) (limit 0) sort)
  "Iterate over a set of data. The collected return values are returned."
  (if sort (setf query (kv (kv "query" query) (kv "orderby" (alist->document sort)))))
  (let ((result (db.find collection query :limit limit :skip skip)))
    (multiple-value-bind (iterator collection docs) (cl-mongo::db.iterator result)
      (loop
         for next = '(NIL (0 1)) then (db.next collection iter)
         for iter = iterator then (nth-value 0 (cl-mongo::db.iterator next))
         until (zerop (length (second next)))
         for idocs = docs then (append idocs (second next))
         finally (setf docs idocs))
      (loop for doc in docs collect (funcall function doc)))))