check resultset for emptiness in clojure jdbc

Question

i'm using clojure with jdbc, compojure, cheshire, postgresql, c3p0, tryin make REST. When i'm using this code as handler

  (defn get-document [id]
      (sql/query (db-connection)
                 ["select * from document where id = cast(? as integer)" id]
                 {:row-fn
                  (fn [first]
                                   (if (empty? first )
                                     (response "empty")
                                     (response first)
                                     ))}))

If reslutset is not empty i have response as i need, but if its empty i got empty brackets [].

Also this is my project dependencies

  :dependencies [[org.clojure/clojure "1.8.0"]
                 [compojure "1.5.1"]
                 [ring/ring-json "0.4.0"]
                 [c3p0/c3p0 "0.9.1.2"]
                 [ring/ring-defaults "0.2.1"]
                 [org.clojure/java.jdbc "0.7.3"]
                 [org.postgresql/postgresql "42.1.4"]
                 [cheshire "5.8.0"]]

Answer 1

The :row-fn function is executed for each row in the result set. When your result set is empty, row-fn is not called.

You may need to use the result of sql/query to handle the response of the query. When there is no result an empty vector is returned (this is []). You can check if the result is empty by calling empty?. Something like this:

(defn get-document [id]
  (let [query ["select * from document where id = cast(? as integer)" id]
        rows  (sql/query (db-connection) query)]
      (if (empty? rows)
        (response "empty")
        (response (first rows)))))