nodejs如何用mongoose从已存在的collection中取出文档记录

testdb中有messages这个集合，但是find不出数据：

var mongoose = require('mongoose'); var db = mongoose.createConnection('mongodb://user:psaawd@localhost:27017/testdb');

db.on('error', console.error.bind(console, 'connection error:')); db.once('open', function callback () { console.log("connection success!"); });

var out = mongoose.model('messages', mongoose.Schema({ name: String}), 'messages'); out.find({}, function(err, data) { console.log(err, data, data.length); });