Minimal query for maps

query.cljs

(ns query.core)

(defn paths
  ([q]
   (paths [] {} q))
  ([current-path m q]
   (letfn [(paths-map
             [current-path m q]
             (apply merge (for [[k v] q]
                            (paths (conj current-path k) {} v))))
           (paths-vec
             [current-path m q]
             (apply merge (for [v q]
                            (if (map? v)
                              (paths-map current-path {} v)
                              (paths (conj current-path v) {} v)))))]
     (cond
       (map? q) (paths-map current-path m q)
       (vector? q) (paths-vec current-path m q)
       :else {q current-path}))))

(defn query-fn
  [q]
  (let [paths (paths q)]
    (fn [db]
      (reduce-kv (fn [m k v] (assoc m k (get-in db v))) {} paths))))

(defn query
  [db q]
  (let [f (query-fn q)]
    (f db)))

(comment
  (query
    {:products/by-id {1 {:product/id 1
                         :product/sku "FINMOD001"
                         :product/nutrition {:energy "100kcal"
                                             :salt "1g"}}}}
    {:products/by-id {1 [:product/id :product/sku :product/nutrition]}})
  #:product{:id 1, :sku "FINMOD001", :nutrition {:energy "100kcal", :salt "1g"}})