Upsert

gistfile1.js

adapter.update = function (model, id, update ,options) {
  var _this = this;
  model = typeof model == 'string' ? this.model(model) : model;
  update = this._serialize(model, update);

  return new Promise(function (resolve, reject) {
    var cb = function (error, resource) {
      if (error) {
        return reject(error);
      }
      _this._handleWrite(model, resource, error, resolve, reject);
    };
    
    if(options){
      model.findByIdAndUpdate(id, update, cb);
    }else{
      model.findByIdAndUpdate(id, update, options, cb);
    }
  });
};