cheshire - Encoding records as JSON objects with additional type field in Clojure -

cheshire's custom encoders seem suitable problem , wrote little helper function:

(defn add-rec-encoder [rec type-token]   (add-encoder rec     (fn [rec jg] (.writestring jg       (str (encode-map (assoc rec :type type-token) jg))))))  (defrecord [a])  (add-rec-encoder "a")  (encode (->a "abc")) 

but produces strange trailing "".

=> {"a":"abc","type":"a"} ""

what causing this? , there approach worth considering (i need able decode record based on type-token)?

(encode-map ... jg) directly writes encoded map json generator jg, returns nil.

this means that, call writestring actually:

(.writestring jg (str nil)) 

which, since (str nil) "", encode , append json generator. correct encoder logic be:

(defn add-rec-encoder [rec type-token]   (add-encoder rec     (fn [rec jg]       (encode-map (assoc rec :type type-token) jg))))