Coercion with the schema

Very often, we want to validate our data against some schema.compojure-api allows us to provide custom schema with constraints for our data.

For our cards entities, we can add the following constraints:

• The name should not be blank and should not have more than 50 characters
• The description should have at least five characters but not more than 100

Create a util.clj file, where we'll include convenience functions:

(ns restful.util
  (:require [clojure.string :as str]))

(def non-blank? (complement str/blank?))

(defn max-length? [length text]
  (<= (count text) length))

(defn non-blank-with-max-length? [length text]
  (and (non-blank? text) (max-length? length text)))

(defn min-length? [length text]
  (>= (count text) length))

(defn length-in-range? [min-length max-length text]
  (and (min-length? min-length text) (max-length? max-length text)))

We'll use these functions to define the schema for CardReqest, in cards.clj:

(ns restful.cards
  (:require [compojure.api.sweet :refer [GET POST PUT DELETE]]
            [restful.models.card :refer [Card]]
            [restful.util :as str]
            [ring.util.http-response :refer [ok not-found created]]
            [schema.core :as s]
            [toucan.db :as db]))

(defn valid-name? [name]
  (str/non-blank-with-max-length? 50 name))

(defn valid-description? [description]
  (str/length-in-range? 5 100 description))

(s/defschema CardRequestSchema
  {:name (s/constrained s/Str valid-name?)
   :description (s/constrained s/Str valid-description?)})

We've defined the schema for CardRequest, which should contain a valid :name and :description.