Tips

Removing Schemas based on a property

Schemas can be walked over recursively using m/walk:

(require '[malli.core :as m])

(def Schema
  [:map
   [:user map?]
   [:profile map?]
   [:tags [:vector [int? {:deleteMe true}]]]
   [:nested [:map [:x [:tuple {:deleteMe true} string? string?]]]]
   [:token [string? {:deleteMe true}]]])

(m/walk
  Schema
  (fn [schema _ children options]
    ;; return nil if Schema has the property 
    (when-not (:deleteMe (m/properties schema))
      ;; there are two syntaxes: normal and the entry, handle separately
      (let [children (if (m/entries schema) (filterv last children) children)]
        ;; create a new Schema with the updated children, or return nil
        (try (m/into-schema (m/type schema) (m/properties schema) children options)
             (catch #?(:clj Exception, :cljs js/Error) _))))))
;[:map
; [:user map?] 
; [:profile map?] 
; [:nested :map]]

In the example, :tags key was removed as it's contents would have been an empty :vector, which is not legal Schema syntax. Empty :map is ok.

Trimming strings

Example how to trim all :string values using a custom transformer:

(require '[malli.transform :as mt])
(require '[malli.core :as m])
(require '[clojure.string :as str])

;; a decoding transformer, only mounting to :string schemas with truthy :string/trim property
(defn string-trimmer []
  (mt/transformer
    {:decoders
     {:string
      {:compile (fn [schema _]
                  (let [{:string/keys [trim]} (m/properties schema)]
                    (when trim #(cond-> % (string? %) str/trim))))}}}))

;; trim me please
(m/decode [:string {:string/trim true, :min 1}] " kikka  " string-trimmer)
; => "kikka"

;; no trimming
(m/decode [:string {:min 1}] "    " string-trimmer)
; => "    "

;; without :string/trim, decoding is a no-op
(m/decoder :string string-trimmer)
; => #object[clojure.core$identity]

Decoding collections

Transforming a comma-separated string into a vector of ints:

(require '[malli.core :as m])
(require '[malli.transform :as mt])
(require '[clojure.string :as str])

(m/decode 
  [:vector {:decode/string #(str/split % #",")} int?] 
  "1,2,3,4" 
  (mt/string-transformer))
; => [1 2 3 4]