A macro wrapping def-record that also defines a constructor function with default values.

make-model.clj

(defmacro make-model
  [name args & body]
  (let [defaults (if (map? (first body)) (first body) {})
        constructor-name (str/lower-case (str "make-" name))]
    `(do (defrecord ~name ~args ~@(if (map? (first body)) (rest body) body))
         (defn ~(symbol constructor-name)
           ([] (~(symbol constructor-name) {}))
           ([values#] (~(symbol (str "map->" name)) (merge ~defaults values#)))))))

Usage like:

(make-model User [firstName lastName] {:lastName "Smith"})
=> #'user/make-user
(make-user {:firstName "John"})
=> #user.User{:firstName "John", :lastName "Smith"}

Default arguments are optional and so too are any arguments to the constructor.

(make-model User [firstName lastName])
=> #'user/make-user
(make-user)
=> #user.User{:firstName nil, :lastName nil}