当使用monger时，我需要提供连接每个请求吗？ [英] When using monger, do I need to supply connection each request?

问题描述

在文档中，mongodb连接建立一次，在使用之前不传递连接对每个命令，是否正确的方式使用monger，或者应该将数据库连接传递给每个调用？

In the documentation, the mongodb connection is established once, before being used without passing the connection to each command, is that the proper way to use monger, or should I pass the database connection to each call?

推荐答案

你使用单个数据库，那么最好设置连接一次：

If you work with single database then it's best to set the connection once:

(mg/connect! db-spec)

但是这不是一个好主意，当你有多个数据库。 Monger有 with-connection 巨集（参阅API文件）：

But it's not a good idea when you have multiple databases. Monger have with-connection macro (see API docs) for this case:

(mg/with-connection db-connection
  ...)

您可以在应用程序初始化期间建立所有连接：

You may establish all connections once during the initialization of your app:

(def conn1 (mg/connect db-spec))

然后使用它们：

(mg/with-connection conn1
  ...)

更新。在我们的应用程序中，数据库连接：

Update. In our application we have a hash-map of all database connections:

(def  ^:dynamic
      ^clojure.lang.PersistentArrayMap
      *connections*
      {})

(defn connect! [db]
  {:pre [(contains? mongo-config db)]}
  (if (-> db *connections* nil?)
      (let [conn (mg/connect (get mongo-config db))]
        (alter-var-root #'*connections*
                        assoc
                        db
                        { :conn conn
                          :db   (mg/get-db conn (name db))})))
  (-> *connections* db :conn))

(defmacro with-db [db & body]
  "Eval body using :amonplus or :statistic db"
  `(mg/with-connection (connect! ~db)
    (mg/with-db        (clojure.core/-> *connections* ~db :db)
      ~@body)))

mongo-config 变量存储我们所有数据库的规范， with-db 宏可以通过名称轻松访问它们：

mongo-config variable stores specification for all our databases and with-db macro makes it easy to access them by their names:

(with-db :my-db
  ...)

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