code: function(req, res, next, relationship) {
  		if(req.fullModel.hasRelationship(relationship)) {
  			return next();
  		}
  
  		return responseUtils.respond(res, 400); //Malformed syntax or a bad query
  	}
docs: Check whether  req.fullModel has relationship
  @param  {ExpressRequest}   req
  @param  {ExpressResponse}   res
  @param  {Function} next         Pass to the next route
  @param  {String}   relationship Relationship name