function based restructuring of clj{s} data
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A Clojure library designed to declaritively reshape data.

Clojars Project

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I often find myself wondering what shape of data is expected by a certain piece of code.

This library sprang forth from those thoughts.

Consider an api that will return to us information about a user. Of course, the information is presented to us in a manner that makes sense for the producer of the data rather than our purpoises. We want to =restructure= the data so that it makes senses for our usecases.

Using restructure we will define a function user-function which will reshape our data the way we want it.

(def user-function
  ;; user-function expects a value like
    {:user_id :rs/id
     :user_info {:user_age_on_date ["_" :rs/age]}}
    ;; and returns a restructured value that matches
    {:id :rs/id :age :rs/age}))

Notice that the exact shape of the incoming data:

  {:user_id  1910191
   :user_info {:user_age_on_date ["ignore me" 10.5]}})
;;=> {:id 1910191, :age 10.5}

If the input is missing a particular key, it will become nil:

(user-function {:user_id  1910191})
;; => {:id 1910191, :age nil}

Other included keys are left alone:

(user-function {:user_id  1910191
                :user_info {:user_age_on_date ["ignore me" 10.5]}
                :user_title "Person"})
;;=> {:id 1910191, :age 10.5, :user_title "Person"}

if you want to ensure the existance of certian keys:

(def safe-user-function
    {:user_id :rs/id
     :user_info {:user_age_on_date ["_" :rs/age]}}
    ;; and returns a restructured value that matches
    {:id :rs/id :age :rs/age}
     #(when (nil? %)
          (ex-info "expected a value for :rs/id" {:value :rs/id})))}))

(safe-user-function {})
;;=>  1. Unhandled clojure.lang.ExceptionInfo
;;=>  expected a value for :rs/id
;;=>  {:value :rs/id}


Note that I used keywords with the rs namespace above. That's actually not nessicary to do.

We can also use sample data to show exactly what we expect to recieve.

(rs {:user_info {:u_id 12345 :u_first_name "Bryan"}
    {:name "Bryan" :id 12345})

The function returned by the prior call to rs is identical to this:

(rs {:user_info {:u_id 0 :u_first_name 1}
    {:name 1 :id 0})


(rs {:user_info {:u_id ::uid :u_first_name ::fn}
    {:name ::fn :id ::uid})

So the user has the flexibility to show what they mean, which is a noble principle to uphold.


Copyright © 2018 Bryan Maass

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.