Clojure using value from another required key in validation

Question

I'm relatively new to clojure and I'm looking for a way to use the value of one required key in the validation of another. I can do it by creating another map with the two values and passing that, but I was hoping there was a simpler way. Thanks

(s/def ::country string?)
(s/def ::postal-code   
  ;sudo-code
  ;(if (= ::country "Canda")
  ;(re-matches #"^[A-Z0-9]{5}$") 
  ;(re-matches #"^[0-9]{5}$"))
)

(s/def ::address
  (s/keys :req-un [
    ::country
    ::postal-code
    ::street
    ::state
  ]))

Answer 1

Here's a way to do it with multi-spec:

(defmulti country :country)
(defmethod country "Canada" [_]
  (s/spec #(re-matches #"^[A-Z0-9]{5}$" (:postal-code %))))
(defmethod country :default [_]
  (s/spec #(re-matches #"^[0-9]{5}$" (:postal-code %))))

(s/def ::country string?)
(s/def ::postal-code string?)
(s/def ::address
  (s/merge
    (s/keys :req-un [::country ::postal-code])
    (s/multi-spec country :country)))

(s/explain ::address {:country "USA" :postal-code "A2345"})
;; val: {:country "USA", :postal-code "A2345"} fails spec: :sandbox.so/address at: ["USA"] predicate: (re-matches #"^[0-9]{5}$" (:postal-code %))
(s/explain ::address {:country "Canada" :postal-code "A2345"})
;; Success!

Another option is and-ing another predicate on your keys spec:

(s/def ::address
  (s/and
    (s/keys :req-un [::country ::postal-code])
    #(case (:country %)
       "Canada" (re-matches #"^[A-Z0-9]{5}$" (:postal-code %))
       (re-matches #"^[0-9]{5}$" (:postal-code %)))))

You might prefer the multi-spec approach because it's open for extension i.e. you can define more defmethods for country later as opposed to keeping all the logic in the and predicate.