Introducing structure with Jan Stępień @janstepien :clojureD, Berlin 2018 

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@cljmuc 

Let’s talk about structure 

Let’s talk about structure of web apps 

Architecture off the shelf 

There are no frameworks* * well, actually 

This is just one recipe 

Ports and adapters Hexagonal Clean 

@janstepien Layered structure 

Domain entities @janstepien 

Use cases and pure logic @janstepien 

Adapters and the outer world @janstepien 

@janstepien Dependencies point only inwards 

Booking tables 

src └── table ├── entities │ └── booking.clj ├── use_cases │ └── book_table.clj └── adapters └── ring.clj Domain entities Use cases Adapters 

(ns table.entities.booking (:require [clojure.spec.alpha :as spec])) (spec/def ::booking (spec/keys :req-un [::name ::seats ::time])) (spec/def ::name string?) (spec/def ::seats (spec/and integer? pos?)) (spec/def ::time inst?) 

(spec/explain ::booking {:name "რუსთაველი" :seats 0 :time #inst "2017-06-06T21:00Z"})) (spec/valid? ::booking {:name "Stępień" :seats 3 :time #inst "2017-06-06T21:00Z" :phone "+49876543210"})) 

(gen/sample (spec/gen ::booking)) #_=> ({:name "ldeDMP9" :seats 3122 :time #inst "1969-12-31T23:59:59.999Z"} {:name "C5bLbvKzGeRt94" :seats 1771071 :time #inst “1970-01-01T00:04:28.571Z"} ...) 

src └── table ├── entities │ └── booking.clj ├── use_cases │ └── book_table.clj └── adapters └── ring.clj Domain entities Use cases Adapters 

(ns table.use-cases.book-table (:require [table.entities.booking :as booking] [clojure.spec.alpha :as spec])) (defn book-table [context booking] {:pre [(spec/valid? ::booking/booking booking)]} (save-booking (:save-booking context) booking)) (defprotocol SaveBooking (save-booking [this booking])) 

(let [booking {:name "Foo Bar" :seats 2 :time (java.util.Date.)} context {:save-booking (reify SaveBooking (save-booking [_ booking] (prn :saved booking)))}] (book-table context booking)) 

src └── table ├── entities │ └── booking.clj ├── use_cases │ └── book_table.clj └── adapters └── ring.clj Domain entities Use cases Adapters 

(ns table.adapters.ring (:require [table.use-cases.book-table :as book-table])) (defn post-booking [req] (let [context (:table/context req) booking (coerce-params (:params req))] (book-table/book-table context booking) {:body "Success!", :status 201)) (defn list-bookings [req] ...) 

(ns table.adapters.ring (:require [compojure.core :as comp :refer [GET POST]])) (defn routes [] (comp/routes (POST "/bookings" [] post—bookings) (GET "/bookings" [] list—bookings))) (defn wrap-context [handler context] (fn [req] (handler (assoc req :table/context context)))) (defn handler [context] (-> (routes) (wrap-context context) ...)) 

src └── table ├── entities │ └── booking.clj ├── use_cases │ └── book_table.clj ├── adapters │ └── ring.clj ├── system │ ├── postgres.clj │ └── http_server.clj └── system.clj @janstepien 

(ns table.system.postgres (:require [com.stuartsierra.component :as component])) (defrecord Postgres [config connection] component/Lifecycle (start [this] (assoc this :connection (connect config))) (stop [this] (close connection) (assoc this :connection nil))) 

(ns table.system.postgres (:require [table.use-cases.book-table :as book-table])) (extend-protocol book-table/SaveBooking Postgres (save-booking [postgres booking] (execute-sql postgres "insert into bookings..." booking))) (defn postgres [config] (map->Postgres {:config config})) 

(ns table.system.http-server (:require [com.stuartsierra.component :as component])) (defrecord HttpServer [handler context server] component/Lifecycle (start [this] (assoc this :server (start-server (handler context)))) (stop [this] (stop-server server) (assoc this :server nil))) (defn http-server [handler] (map->HttpServer {:handler handler})) 

(ns table.system (:require [com.stuartsierra.component :as component] [table.system [http-server :as http] [postgres :as postgres]] [table.adapters.ring :as ring])) (defn system [config] (component/system-map :postgres (postgres/postgres config) :context (component/using {} {:save-booking :postgres}) :http (component/using (http/http-server ring/handler) {:context :context}))) 

src └── table ├── entities │ └── booking.clj ├── use_cases │ └── book_table.clj ├── adapters │ └── ring.clj ├── system │ ├── postgres.clj │ └── http_server.clj ├── system.clj └── main.clj @janstepien 

(ns table.main (:require [com.stuartsierra.component :as component] [table.system :as system])) (defn -main [] (let [config {:postgres {:host "localhost" :user "foo" :password "bar"} :http {:port 8080}}] (component/start (system/system config)))) 

src └── table ├── entities │ └── booking.clj ├── use_cases │ └── book_table.clj ├── adapters │ └── ring.clj ├── system │ ├── postgres.clj │ └── http_server.clj ├── system.clj └── main.clj 

clojure.spec for contracts Ring and Compojure for HTTP Component and System for lifecycle Luminus or Duct for a framework 

Introducing structure with Jan Stępień @janstepien :clojureD, Berlin 2018