在环/ compojure webapp中使用LevelDB [英] Using LevelDB in a ring/compojure webapp

问题描述

我正在尝试在一个ring / compojure应用程序中设置LevelDB，并寻找一个惯用的方法来访问每个请求中打开的db描述符。

I am am trying to setup LevelDB in a ring/compojure app, and looking for an idiomatic way to to access the opened db descriptor into each request.

例如：

(defn -main
  "I don't do a whole lot ... yet."
  [& args]

  (println "Opening LevelDB file in db/main")
  (with-open [main-db (db/open "db/main")]

    (println "Running server on port 3000")
    (run-jetty #'web/app {:port 3000})))

如何访问 main-db 描述符到请求处理程序中？

How do you access the main-db descriptor into the request handlers?

即

(defroutes handler

  (GET "/test" []
    (db/put main-db (.getBytes "testKey2") (.getBytes "testValue2"))
    "<h1>Hello World</h1>")

PS：我使用Sedward的leveldb-clj lib并将其打包成clojar： https://clojars.org/org.clojars.aircart/leveldb-clj p>

PS: I am using the leveldb-clj lib from Sedward and packaged it into a clojar: https://clojars.org/org.clojars.aircart/leveldb-clj

推荐答案

如果你想在应用程序中有一个全局描述符，最简单的选项可能是在顶层存储promise或延迟Var：

If you want a single global descriptor in your app, the simplest option might be to store a promise or delay in a top-level Var:

(def level-db-descriptor (promise))

(defn open [...]
  ...
  (deliver level-db-descriptor ...))

(open ...)

;; or

(def level-db-descriptor (delay (open ...)))

然后，当你需要得到它时，请说 @ level-db-descriptor 。

Then say @level-db-descriptor when you need to get at it.

是不是很大，如果你需要偶尔替换描述符;您可以同时保留 @ level-db-descriptor 使用模式：

This is not that great if you need to replace the descriptor occasionally; you can, however, support that too while preserving the @level-db-descriptor pattern of usage:

(defprotocol PDescriptorBox
  (put-descriptor! [this d])
  (get-descriptor [this]))

(defn make-descriptor-box []
  (let [box (clojure.lang.Box. nil)]
    (reify
      clojure.lang.IDeref
      (deref [this] (get-descriptor this))
      PDescriptorBox
      (get-descriptor [this]
        (locking this
          (.-val box)))
      (put-descriptor! [this d]
        (locking this
          (set! (.-val box) d))))))

你可以用更复杂的东西替换 put-descriptor！（当然也可以用旧的做一些新的描述符） 。

You could replace put-descriptor! with something more sophisticated, of course (perhaps producing a new descriptor only after doing something with the old one).

如果您希望能够并行运行应用程序的多个实例，那么这些单独的实例可能会使用某种状态容器，您可能需要使用它们来存储您的描述符，而不是顶级Vars。

If you want to be able to run multiple instances of your app in parallel, then those individual instances will likely use some sort of state containers and you'll probably want to use those to store your descriptors rather than top-level Vars.

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