noir framework: a middleware for jdbc-connection-handling (using c3p0 connection pool)

jdbc.clj

(ns my-web-app.middleware.jdbc
  (:require 
    [clojure.java.jdbc :as jdbc]
    [noir.options :as options])
  (:import com.mchange.v2.c3p0.ComboPooledDataSource))

(defn- pooled-data-source
  [db-connection-settings]
  (let [cpds (doto (ComboPooledDataSource.)
               (.setDriverClass (:classname db-connection-settings)) 
               (.setJdbcUrl (str "jdbc:" (:subprotocol db-connection-settings) ":" (:subname db-connection-settings)))
               (.setUser (:user db-connection-settings))
               (.setPassword (:password db-connection-settings))
               ;; expire excess connections after 30 minutes of inactivity:
               (.setMaxIdleTimeExcessConnections (* 30 60))
               ;; expire connections after 3 hours of inactivity:
               (.setMaxIdleTime (* 3 60 60)))] 
    {:datasource cpds}))

(def ^{:arglists ([db-connection-settings])} pooled-data-source-as-singleton
  (memoize pooled-data-source)) 

(def pooled-data-source-as-singleton
  (memoize pooled-data-source)) 

(defn wrap-jdbc-connection [handler]
  (fn [request]
    (jdbc/with-connection 
      (pooled-data-source-as-singleton (options/get :db-connection-settings))
      (handler request))))
    
    

project.clj

(defproject my-web-app
    ...
    [org.clojure/java.jdbc "0.0.6"]
    [c3p0/c3p0 "0.9.1.2"]
    [hsqldb/hsqldb "1.8.0.10"]]
    ...

server.clj

(ns my-web-app.server
  (:require 
    [my-web-app.middleware.jdbc :as jdbc]
    [noir.server :as server]))

(def ^:private db-connection-settings {:classname "org.hsqldb.jdbcDriver"
	:subprotocol "hsqldb"
	:subname "db/test-db"})

(server/load-views "src/order_manager/views/")

(server/add-middleware jdbc/wrap-jdbc-connection)

(defn -main [& m]
  (let [mode (keyword (or (first m) :dev))
        port (Integer. (get (System/getenv) "PORT" "8080"))]
    (server/start port {:mode mode
                        :ns 'my-web-app
                        :db-connection-settings db-connection-settings})))

Links

*http://webnoir.org/tutorials/middleware
*http://github.com/clojure/java.jdbc/blob/master/doc/clojure/java/jdbc/ConnectionPooling.md