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@abp abp/draft.txt
Last active Dec 13, 2015

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Every request is an endpoint to start some computation.
The input is the request, the output is the response.
Typical stages between those are:
Parsing, validation, storage, retrieving stored data and rendering an output.
Based on Ring and Compojure, we do the following to integrate routes with
Prismatic Graph:
Compojure matches the request against routes, calling the route handlers,
until a non nil result is returned.
Routes for integration with the Graph return route-keys,
singular :key or nested like [:some :key].
A graph computation is then invoked, to calculate a result
for the given route-keys, based on the request.
Due to the declarative nature of the graph, the route now *depends* on
it's outputs, rather than explicitly needing to build them.
To separate routes that dispatch onto the graph from regular ones, there
is a wrap-graph-dispatch middleware. It takes up to three parameters:
handler - We know this one.
app-graph - The graph to invoke.
context-keys - Optional. Keys to be prepended to route-keys in this context.
(think context-keys [:context :to] route-keys [:some :key]
=> [:context :to :some :key]).
Now we can compute the route from the graph, by feeding the request data
to the graph, pulling out the route-keys as result.
When compiled for lazy excecution, the graph will only resolve
route-keys dependencies.
If the computation returns nil, the next routes are matched, just like
with regular Compojure routes.
(ns web-grapp
(:require [plumbing.core :refer :all]
[plumbing.graph :as graph]
[compojure.core :refer :all]
[compojure.response :refer [render]]
[hiccup.page :refer [html5]]
[robert.hooke :refer [with-scope add-hook]]))
(defn graph-dispatch [f ks request]
(get-in ((::graph request) request)
(concat (::context-keys request)
(cond-> ks
(nil? ks) vec
(keyword? ks) vector))))
(defn wrap-graph-dispatch
([handler app-graph]
(wrap-graph-dispatch handler app-graph nil))
([handler app-graph context-keys]
(let [context-keys (cond-> context-keys
(nil? context-keys) vec
(keyword? context-keys) vector)]
(fn [request]
(render
(with-scope
(add-hook #'render ::wrap-graph-dispatch #'graph-dispatch)
(handler (assoc request
::graph app-graph
::context-keys context-keys)))
request)))))
(def search-graph
{:db {:search (fnk [[:params q]]
["some" "results"])}
:view {:search-results (fnk [[:db search] [:params q]]
(list [:p "Results for query: " q]
[:ul (for [result search]
[:li result])]))}
:routes {:search (fnk [[:view search-results]]
(html5 search-results))}})
(def lazy-search (graph/lazy-compile search-graph))
;; (wrap-graph-dispatch (GET "/search" _ :search) lazy-search :routes))
(defroutevec search
[:routes
#get :search])
(search {:uri "/search" :request-method :get :params {:q "a query"}})
;; {:status 200,
;; :headers {"Content-Type" "text/html; charset=utf-8"},
;; :body
;; "<!DOCTYPE html>\n<html><p>Results for query: a query</p><ul><li>some</li><li>results</li></ul></html>"}
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