Malli decoders are very cool. But as far as I understand, in order to use a schema that relies on decoders, clients have to decode data before validating it. It means that a schema that relies on decoders cannot be used as-is for validating data. Am I correct?

For now, that’s true. There was a discussion some time ago to add :parsed schema element. That would just run m/-parse in before validate, explain, transform etc. like s/conform on spec. Could also be :decoded, so that this would work:

(m/validate [:decoded {:decode :string} schema] "ip/127.0.0.1") ; => true

you can do that “easily” in the user space too. Just a wrapper-schema basically.

@ikitommi Here is my attempt to write a parser in user space:

(defn my-parse
  [schema data]
  (let [data' (decode schema data (transformer string-transformer default-value-transformer))]
    (if (validate schema data')
      (encode schema data' (transformer string-transformer default-value-transformer))
      (humanize (explain schema data')))))

(def schema 
  [:map
   [:count :int]
   [:asset-id [:multi {:dispatch first
                     :decode/string #(str/split % #"/")
                     :encode/string #(str/join "/" %)}
             ["domain" [:tuple  [:= "domain"] domain]]
             ["ip" [:tuple {:error/message "Invalid IP"} [:= "ip"] ipv4]]]]])

(my-parse schema {:count 12
                  :asset-id "ip/127.0.0.1"})
;; {:count "12", :asset-id "ip/127.0.0.1"}
;; Oops "12" instead of 12

just return the original instead of encode the whole value into string-domain?

because:

(m/encode :int 1 mt/string-transformer) ; => "1"

… or create a custom name for the parsing transformer, e.g. :parse - it’s it a name you have defined, it doesn’t transform anything else.

(let [schema [:map
              [:x :int]
              [:y [:int {:decode/parse (partial + 10)
                         :encode/parse (partial * 2)}]]]
      t (mt/transformer {:name :parse})]
  (as-> (m/decode schema {:x 0, :y 0} t) $
        (m/encode schema $ t)))
;; => {:x 0, :y 20}

I cannot return the original as I would like the default values to be added by the parser. For instance, with a schema that assigns 42 as a default value to :count

(def schema 
  [:map
   [:count [:int {:default 42}]]
   [:asset-id [:multi {:dispatch first
                     :decode/string #(str/split % #"/")
                     :encode/string #(str/join "/" %)}
             ["domain" [:tuple  [:= "domain"] domain]]
             ["ip" [:tuple {:error/message "Invalid IP"} [:= "ip"] ipv4]]]]])

(my-parse schema {:asset-id "ip/127.0.0.1"})
;; {:asset-id "ip/127.0.0.1", :count "42"}

However, I really like the idea of a custom name

We need that as our plan is to have a company wide schema repository to be consumed by all apps

Is there an option for MapSchemas to skip generating specific field/s?

I might have encountered a bug:

{:example/user   [:map {:fully/entity?   true
                        :fully.entity/id :user/id}
                  [:user/id :uuid]
                  [:user/username :string]
                  [:user/password :string]
                  [:user/email :string]]}

(m/schema type {:registry registry})

(m/properties (m/schema type {:registry registry}))