Mongoose toArray（）未定义

Question

通过mongo和mongoose进行连接时有什么区别？因为这段代码能够找到我的文档。

var MongoClient = require('mongodb').MongoClient;

// Connect to the db
MongoClient.connect("mymongourl", 
function (err, db) {
  if (err) {
    return console.dir(err);
  }

  var asset = db.collection('assets');
  asset.find({
    name: 'John'
  }).toArray(function (err, items) {
    console.log(items);
  });
});

但是这段代码给了我'TypeError：无法读取属性'toArray'of undefined'

   var mongoose = require('mongoose');
   mongoose.connect('mymongourl');
   var db = mongoose.connection;

  var asset = db.collection('assets');
  asset.find({
    name: 'John'
  }).toArray(function (err, items) {
    console.log(items);
  });