Return an error if query parameter is missing.

clj/clarity/clarity/server.clj

(defn read-tx-data [str]
  (edn/read-string {:readers {'db/id (partial apply d/tempid)}} str))
(defn http-error [status body & {:as attrs}]
  (into {:status status
         :body body}
        attrs))
(defroutes app-routes
  (GET "/" []
       {:status 200
                     [:textarea {:name "facts" :cols 80 :rows 20}]
                     [:input {:type "submit" :value "transact!"}]])})
  (GET "/facts" {{query :q} :params}
       (pr-str (d/q (edn/read-string query) (d/db conn))))
       (if query
         (pr-str (d/q (edn/read-string query) (d/db conn)))
         (http-error 400 (pr-str {:error "Missing required `q` parameter"}))))
  (POST "/facts" [facts]
        (pr-str (d/transact conn (read-tx-data facts)))))