When should i be opening and closing MongoDB connections?

Question

i am very new to MongoDB and NoSQL in general and i've just started building a site with MongoDB / Norm / ASP.NET MVC 3.

I am wondering how i should be scoping the connections to my Mongo database.

Right now i have a Basecontroller that instanciates the MongoSession and onActionExecuted i dispose it so all my deriving controllers will have access to my MongoSession. The MongoSession class opens a connection in its constructor and disposes it on Dispose(), the way it's working today.

private IMongo _mongo;

public MongoSession()
{         
    _mongo = Mongo.Create("connString");      
} 

public void Dispose()
{
    _mongo.Dispose();
}

I am a bit worried it might be holding connections open too long if i am doing other stuff aswell in the controllers.

Is that approach enought to not risking holding too many connections open or should i be doing something more like the example method below?

   public void Add<T>(T item) where T : class, new()
   {
       using (var mongo = Mongo.Create("connString"))
       {
         mongo.GetCollection<T>().Insert(item); 
       }
   }

Another follow up question is:

Are opening and closing MongoDB connections through Norm "expensive" operations?

Answer 1

I would leave the connection open as re-creating the connection is costly. Mongo is fine with lots of connections, open for a long time. What you ideally should do is to share the connection with all parts of your application as a persistent connection. The C# driver should be clever enough to do this itself, so that it does not create too many connections, as internally it uses "connection pooling" that makes it even re-use connections. The docs say: "The connections to the server are handled automatically behind the scenes (a connection pool is used to increase efficiency)."

cheers, Derick