Reading from a remote MongoDB server

In many cases, it may be more feasible to set up a MongoDB instance on a remote machine. This recipe will cover how to obtain data from a MongoDB hosted remotely.

Getting ready

We should create a remote database. MongoLab (https://mongolab.com) and MongoHQ (http://www.mongohq.com) offer MongoDB as a service and have free options to set up a small development database.

Tip

These services will require us to accept their terms and conditions. For some of us, it may be best to host the database in our own remote server.

Install the MongoDB package from Cabal as follows:

$ cabal install mongoDB

Also, install the helper following helper libraries as follows:

$ cabal install split
$ cabal install uri

How to do it...

1. Use the OverloadedString and ExtendedDefaultRules language extensions required by the library. Import helper functions as follows:

   {-# LANGUAGE OverloadedStrings, ExtendedDefaultRules #-}
   import Database.MongoDB
   import Text.URI
   import Data.Maybe
   import qualified Data.Text as T
   import Data.List.Split

2. Specify the remote URI for the database connection as follows:

   mongoURI = "mongodb://user:pass@ds12345.mongolab.com:53788/mydb"

3. The username, password, hostname, port address number, and database name must be extracted from the URI, as presented in the following code snippet:

   uri = fromJust $ parseURI mongoURI
   
   getUser = head $ splitOn ":" $ fromJust $ uriUserInfo uri
   
   getPass = last $ splitOn ":" $ fromJust $ uriUserInfo uri
   
   getHost = fromJust $ uriRegName uri
   
   getPort = case uriPort uri of 
       Just port -> show port 
       Nothing -> (last.words.show) defaultPort
   
   getDb = T.pack $ tail $ uriPath uri

4. Create a database connection by reading the host port of the remote URI as follows:

   main :: IO ()
   main = do
       let hostport = getHost ++ ":" ++ getPort
       pipe <- runIOE $ connect (readHostPort hostport)
       e <- access pipe master getDb run
       close pipe
       print e

5. Optionally authenticate to the database and obtain data from the "people" collection as follows:

   run = do
     auth (T.pack getUser) (T.pack getPass)
     getData
   
   getData = rest =<< find (select [] "people") {sort=[]}

See also

If the database is on a local machine, refer to the Using MongoDB queries in Haskell recipe.