Question

I am implementing a simple drop-down using hiccup:

;DATASET/CREATE
(defn get-cols-nms [table] 
      "This function gets the list of columns of a specific table".
  (do (db/cols-list table)))

(defpartial form-dataset [cols-list]
  (text-field "dataset_nm" "Input here dataset name")[:br]
  (drop-down "table" tables-n)
  (submit-button "Refresh")[:br]
  (mapcat #(vector (check-box %) % [:br]) cols-list) 
  )

(defpage "/dataset/create" []
  (common/layout
    (form-to [:post "/dataset/create"]
      (form-dataset (get-cols-nms (first tables-n))))))

(defpage [:post "/dataset/create"] {:as ks}
  (common/layout
    (let [table (ks :table)]
      (form-to [:post "/dataset/create"] 
    (form-dataset (get-cols-nms table))))))

What I need is to issue a post request (as I think this the only way to do it, but I am open to suggestions) when the drop-down is selected on a specific table (so that “get-cols-nms” gets called with the selected table). In this way, when a table of the database is selected in the drop-down, the table columns will be automatically showed.

So, ultimately, the main point is for me to understand better this function:

 (drop-down "table" tables-n) 

I think that to do what I want I need the tag to have an “onchange” attribute that calls a javascript function. But I don’t know: 1) if I can do this using the hiccup form-helper drop-down; 2) how can I issue (if this is the only solution, maybe there is an hiccup way?) a post request with javascript.

==EDIT==

Following the answer to this question, I rewrote the code above.It should be pretty straightforward. As I think there are not so many examples of hiccup out there, I will post my code here for reference.

Please, bear in mind that there is still a problem with this code: the drop-down won’t stay on the selected item, but it will return at the default. This is because it submits “onchange”. I still could not find a solution for that, maybe somebody could help…

;DATASET/CREATE
(defn get-cols-nms [table] 
  (do (db/cols-list table)))

(defpartial form-dataset [cols-list]
  (text-field "dataset_nm" "Input here dataset name")[:br]
  (assoc-in (drop-down "table" tables-n) [1 :onclick] "this.form.submit()")[:br]
  [:input {:type "submit" :value "Submit" :name "name"}][:br]
  (mapcat #(vector (check-box %) % [:br]) cols-list) 
  )

(defpage "/dataset/create" []
  (common/layout
    (form-to [:post "/dataset/create"]
      (form-dataset(get-cols-nms (first tables-n))))))

(defpage [:post "/dataset/create"] {:as ks}
  (common/layout
    (prn ks)
    (let [table (ks :table)]
      (form-to [:post "/dataset/create"] 
    (if (= (:name ks) nil)
    (form-dataset (get-cols-nms table))
    [:p "It works!"])))))

Answer 1

hiccup.form-helpers/drop-down doesn’t directly support adding attributes to its select element, but it does guarantee there is a standard hiccup attribute map in its return value – meaning the attributes are a map at index 1 (the second element) of the returned vector.

That means you can do something like

(assoc-in (drop-down ....) [1 :onchange] "this.form.submit()")

to generate a select tag with an onchange property.