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Router

Routes are just data and to do routing, we need a router instance satisfying the reitit.core/Router protocol. Routers are created with reitit.core/router function, taking the raw routes and optionally an options map.

The Router protocol:

(defprotocol Router
  (router-name [this])
  (routes [this])
  (options [this])
  (route-names [this])
  (match-by-path [this path])
  (match-by-name [this name] [this name params]))

Creating a router:

(require '[reitit.core :as r])

(def router
  (r/router
    ["/api"
     ["/ping" ::ping]
     ["/user/:id" ::user]]))

Name of the created router:

(r/router-name router)
; :mixed-router

The flattened route tree:

(r/routes router)
; [["/api/ping" {:name :user/ping}]
;  ["/api/user/:id" {:name :user/user}]]

With a router instance, we can do Path-based routing or Name-based (Reverse) routing.

More details

Router options:

(r/options router)
{:lookup #object[...]
 :expand #object[...]
 :coerce #object[...]
 :compile #object[...]
 :conflicts #object[...]}

Route names:

(r/route-names router)
; [:user/ping :user/user]

The compiled route tree:

(r/routes router)
; [["/api/ping" {:name :user/ping} nil]
;  ["/api/user/:id" {:name :user/user} nil]]

Composing

As routes are defined as plain data, it's easy to merge multiple route trees into a single router

(def user-routes
  [["/users" ::users]
   ["/users/:id" ::user]]) 

(def admin-routes
  ["/admin"
   ["/ping" ::ping]
   ["/users" ::users]]) 

(r/router
  [admin-routes
   user-routes])

Merged route tree:

(r/routes router)
; [["/admin/ping" {:name :user/ping}]
;  ["/admin/db" {:name :user/db}]
;  ["/users" {:name :user/users}]
;  ["/users/:id" {:name :user/user}]]

More details on composing routers.

Behind the scenes

When router is created, the following steps are done:

  • route tree is flattened
  • route arguments are expanded (via :expand option)
  • routes are coerced (via :coerce options)
  • route tree is compiled (via :compile options)
  • route conflicts are resolved (via :conflicts options)
  • optionally, route data is validated (via :validate options)
  • router implementation is automatically selected (or forced via :router options) and created
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