如何使此代码更加通用/简洁？

Question

我有几个请求处理程序，它们都有相似的格式。

(defn handle-data-1
  [req]
  {:pre [(some? req)]}
  (try
    (let [start-date (parse-query-param (-> req :params :start-date))
          end-date (parse-query-param (-> req :params :end-date))
          data (db/fetch-data-1 start-date end-date)
          data-count (count data)]
      (log/debugf "data-count=%d start-date=%s end-date=%s" data-count start-date end-date)
      (if (pos? data-count)
        {:status 200
         :body data}
        {:status 404}))
    (catch Exception e
      (let [error-message (.getMessage e)]
        (log/errorf "%s" error-message)
        {:status 500 :body error-message}))))

(defn handle-data-2
  [req]
  {:pre [(some? req)]}
  (try
    (let [limit (Long/valueOf (parse-query-param (-> req :params :limit)))
          data (db/fetch-data-2 limit)
          data-count (count data)]
      (if (pos? data-count)
        {:status 200
         :body data}
        {:status 404}))
    (catch Exception e
      (let [error-message (.getMessage e)]
        (log/errorf "%s" error-message)
        {:status 500 :body error-message}))))

(defn handle-data-3
  [_]
  (try
    (let [data (db/fetch-data-3)
          data-count (count data)]
      (log/debugf "data-count=%d" data-count)
      (if (pos? data-count)
        {:status 200
         :body data}
        {:status 404}))
    (catch Exception e
      (let [error-message (.getMessage e)]
        (log/errorf "%s" error-message)
        {:status 500 :body error-message}))))

我正在尝试创建一个通用函数，该函数可以被所有处理程序函数使用。类似于：

(defn try-query [f]
  {:pre [(some? f)]}
  (try
    (let [data (f) ;; <- need to invoke function and store results in data
          data-count (count data)]
      (if (pos? data-count)
        {:status 200
         :body data}
        {:status 404}))
    (catch Exception e
      (let [error-message (.getMessage e)]
        (log/errorf "%s" error-message)
        {:status 500 :body error-message}))))

(defn handle-data-1 [req]
  (let [start-date (parse-query-param (-> req :params :start-date))
        end-date (parse-query-param (-> req :params :end-date))]
    (log/debugf "start-date=%s end-date=%s" start-date end-date)
    (try-query (fn [] (db/fetch-data-1 start-date end-date))))) ;; 

此通用函数需要以另一个函数（或闭包）作为参数，并且可以具有可变的参数数量。我希望这个通用函数可以调用传入的函数，并将结果存储在一个变量中。

在Ruby中，我可以通过向函数传递lambda函数来实现，然后在函数内部调用lambda函数。我不确定如何在Clojure中实现。

有什么想法吗？

Comments

现在它已经工作了。我相信原始的`Cannot open <nil> as a Reader`错误是由于调用链中缺少解引用所引起的。

我将函数移动到let中以便清理一下。

(defn handle-data-1 [req]
  (let [start-date (parse-query-param (-> req :params :start-date))
        end-date (parse-query-param (-> req :params :end-date))
        query-fn (fn [] (db/fetch-data-1 start-date end-date)]
    (log/debugf "start-date=%s end-date=%s" start-date end-date)
    (try-query query-fn))))

Answer 1

Comments

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我认为这个错误可能是因为在调用链中遗漏了解引用导致的。