connect / disconnect to mongo db when app boots and then reuse connection in my functions

[Ben McFerren]

newbie question but I'm having trouble finding a definitive answer online

so far, I have been connecting to my mongodb in the let block of each of my function definitions.

(def mongo-uri "mongodb://<username:<password>@...")

(defn get-node [nodeid]
  (let [_nodeid nodeid
        uri mongo-uri
            {:keys [conn db]} (mg/connect-via-uri uri)
        ncoll "nodes"]


    (mc/find-maps db ncoll {:_id _nodeid})  
))

after some research, I found out this may be why my app is running slow with my compose service: http://stackoverflow.com/questions/32539191/connecting-to-remote-mongodb-quite-slow

I found a few sources online that discuss how to reuse the connection but I am having trouble finding a example online that shows me how my function definitions can have access to the connection object if the let block is not nested inside the function definition. 

http://stackoverflow.com/questions/23945557/mongodb-connection-pattern-using-monger

http://clojuremongodb.info/articles/connecting.html#supported_connection_options

For example:

(let [uri               "mongodb://clojurewerkz/monger!:monger!@127.0.0.1/monger-test4"
      {:keys [conn db]} (mg/connect-via-uri "mongodb://127.0.0.1/monger-test4")])

Could you please help me find the correct syntax to use so that my functions can have access to reuse the connection?

I am very grateful for help you can offer.

All the best,

Ben

[Fernando Dobladez]

Looks like what you want is to establish the connection when your app starts, keep a reference to that connection on a shared namespace and simply refer to it from your functions.

You can keep a reference to the connection in a var as in `(def conn ...)`, either directly or using an `(atom)`.

Now, this may be enough for small "scripts". However, for non-trivial apps you'd want something more sophisticated:

* https://github.com/stuartsierra/component

* https://github.com/danielsz/system

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[Ben McFerren]

can you please write out some example symtax using (def conn ... as well as (atom) along with connecting by uri?

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