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Adding keys to the request map
Keys can be added to the request map to pass additonal information to the handler and other middleware.
Here is an example that adds a
:user key to the request, if there is a user ID in the session.
(defn wrap-user [handler] (fn [request] (if-let [user-id (-> request :session :user-id)] (let [user (get-user-by-id user-id)] (handler (assoc request :user user))) (handler request))))
get-user-by-id function will depend on how the application stores user information.
Wrapping the handler in a binding
Often it is useful to bind an object to a var for the duration of a handler.
Here is an example that wraps a handler in the (now deprecated) clojure.contrib.sql/with-connection macro.
(defn wrap-sql-connection [handler db-spec] (fn [request] (with-connection db-spec (handler request))))
Conditionally executing the handler
(defn wrap-auth [handler] (fn [request] (if (authorized? request) (handler request) (-> (response "Access Denied") (status 403)))))