SQL helper function

gistfile1.clj

(ns db-util
  (:require [clojure.string :as str]))

(def ^:private placeholders-for (comp (partial str/join ",") #(repeat % '?) count))

(defn in-statement
  "Takes a prepared SQL statement and variable number of arguments, which may be
   also collection values. Replace all occurences of IN (?) with spliced out values
   such as IN (?,?,?) where number of placeholder characters is the same as count
   of elements in corresponding argument which is assumed to be a collection.
   In case that collection argument has only one element, IN (?) is transformed
   into more effective = ? form. Placeholders in query which don't corresponds to
   collection arguments are unnafected. Returns vector, with first item of the
   vector as transformed prepared SQL statement and rest as spliced out arguments."
  [statement & args]
  (let [in-placeholders-positions (->> (re-seq #"\?|IN \(\?\)" statement)
                                       (map vector (iterate inc 0))
                                       (filter #(= (second %) "IN (?)"))
                                       (map first)
                                       (set))
        in-placeholders-args (->> args
                                  (map vector (iterate inc 0))
                                  (filter #(contains? in-placeholders-positions (first %)))
                                  (map second))
        expanded-statement (reduce (fn [acc arg]
                                     (str/replace-first acc #"IN \(\?\)"
                                                        (if (> (count arg) 1)
                                                          (str "IN (" (placeholders-for arg) ")")
                                                          "= ?")))
                                   statement in-placeholders-args)
        unspliced-args (->> args
                            (map #(if (coll? %) (seq %) %))
                            (flatten))]
    (into [] (cons expanded-statement unspliced-args))))

;; following holds true
(= (in-statement "id = ? AND user_id IN (?) AND msg_id IN (?)" 1 #{2 3 4} #{5})
   ["id = ? AND user_id IN (?,?,?) AND msg_id = ?" 1 2 3 4 5])