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advanced_usage.md

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Advanced usage

The following covers more experimental use of SimpleUI in dynamic forms. Dynamic forms are those which grow as you fill them out, a good example is the profile builder on LinkedIn.

Component stack

SimpleUI retains a call stack of nested components. This is used to set ids and values in the sections below.

ids and values

In the introductory example we used a fixed id #hello. If a component exists multiple times you may set id automatically.

[:div.my-component {:id id} ...]

SimpleUI also provides optional path and value functions.

[:input {:type "text" :name (path "first-name") :value (value "first-name")}]
[:input {:type "text" :name (path "last-name") :value (value "last-name")}]

These are unique for each instance of a component and make it easy to retain state over stateless http requests.

Note: path and value only work when id is set at the top level of the component. SimpleUI uses id to record the position of the component in the component stack.

Casting values

You may parameter cast within the body of defcomponent

[:div
  (if ^:boolean (value "grumpy")
    "Cheer up!"
    "How are you?")]

Component Arrays

If you are using the component stack on a page, you must invoke simpleui.rt/map-indexed instead of clojure.core/map. This is because the index of the array forms part of the component stack.

(def data [{:first-name "Fred" :last-name "Smith"}
           {:first-name "Ocean" :last-name "Leader"}])

(defcomponent table-row [req index first-name last-name]
  [:tr ...])

...

[:table
  (rt/map-indexed table-row req data)]

relative paths

path and value are set based on the position of each component on the stack. It is sometimes useful to reference other components

(value "subcomponent\\parameter") ;; naughty naughty!
(value "..\\sibling-component\\parameter")

Be careful when using simpleui.rt/map-indexed

;; called from within array component
(value "..\\..\\sibling-component\\parameter")

We need to ascend two levels in the stack because the array index counts as one level. We can also use absolute paths for simple parameters not in the component stack.

(when (= (value "\\parameter-without-path") "do")
  ...)

Transforming parameters to JSON

htmx submits all parameters as a flat map, however we can use the path components stack to transform it into nested json for database access etc. Simply call simpleui.form/json-params

(json-params
  {:store-name "My Store"
   :0_customers_first-name "Joe"
   :0_customers_last-name "Smith"
   :1_customers_first-name "Jane"
   :1_customers_last-name "Doe"})

;; {:store-name "My Store"
;;  :customers [{:first-name "Joe" :last-name "Smith"}
;;              {:first-name "Jane" :last-name "Doe"}]}

simpleui.form/flatten-json reflattens the nested structure.

Prebind

Prebind is applied to req before the arguments are bound on defcomponent. It can be used in the following way

(defcomponent ^{:req my-prebind} my-component [req arg1 arg2] ...)

Prebind can be applied in different ways

  • ^{:req prebind} prebind is applied to entire req object (prebind req)
  • ^{:params prebind} prebind is applied to the JSON Nested params. (prebind json-params req)
  • ^{:params-stack prebind} prebind is applied to the JSON Nested params at the current point in the component stack.

For components with multiple arguments, prebind will not be applied when the multi-arg version is invoked.