code: function (connection, collections, cb) {
  
        if (!connection.identity) return cb(Errors.IdentityMissing);
        if (connections[connection.identity]) return cb(Errors.IdentityDuplicate);
  
        // Store the connection
        connections[connection.identity] = {
          config: connection,
          collections: collections,
          client: null
        };
  
  
        // connect to database
        new Connection(connection, function (err, client) {
  
          if (err) return cb(err);
  
          connections[connection.identity].client = client;
  
          // Build up a registry of collections
          Object.keys(collections).forEach(function (key) {
            connections[connection.identity].collections[key] = new Collection(collections[key], client);
          });
  
          // execute callback
          cb();
        });
  
      }
docs: Register a connection and the collections assigned to it.
  
  @param  {Connection} connection
  @param  {Object} collections
  @param  {Function} cb