mongoose.connection（）和mongoose.createConnection（）之间的混淆

Question

我研究猫鼬已经三天了，对这两种方法的使用我有点困惑（我知道将来会不推荐使用“ mongoose.connection（）” …）

问题是：当我尝试转换（从“ mongoose.connection（）”到“
mongoose.createConnection（）”）此示例的action.js文件https://gist.github.com/2785463时，不为我工作…

有我的代码…

var mongoose = require('mongoose'),
db = mongoose.createConnection('localhost', 'test');

db.on('error', function () {
  console.log('Error! Database connection failed.');
});

db.once('open', function (argument) {
  console.log('Database connection established!');

  mongoose.connection.db.collectionNames(function (error, names) {
    if (error) {
      console.log('Error: '+ error);
    } else {
      console.log(names);
    };
  });
});

这是我的终端输出（在我的ubuntu终端上键入“ node test.js”。）

Database connection established!

/home/_user_/Scrivania/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/server.js:437
    throw err;
          ^
TypeError: Cannot call method 'collectionNames' of undefined
  at NativeConnection.<anonymous> (/home/_user_/Scrivania/test2.js:11:25)
  at NativeConnection.g (events.js:192:14)
  at NativeConnection.EventEmitter.emit (events.js:93:17)
  at open (/home/_user_/Scrivania/node_modules/mongoose/lib/connection.js:408:10)
  at NativeConnection.Connection.onOpen (/home/_user_/Scrivania/node_modules/mongoose/lib/connection.js:415:5)
  at Connection._open (/home/_user_/Scrivania/node_modules/mongoose/lib/connection.js:386:10)
  at NativeConnection.doOpen (/home/_user_/Scrivania/node_modules/mongoose/lib/drivers/node-mongodb-native/connection.js:47:5)
  at Db.open (/home/_user_/Scrivania/node_modules/mongoose/node_modules/mongodb/lib/mongodb/db.js:287:14)
  at Server.connect.connectCallback (/home/_user_/Scrivania/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/server.js:235:7)
  at g (events.js:192:14)

Answer 1

如果你不叫mongoose.connect()，然后mongoose.connection不包含的开放连接。您应该改用mongo.createConnection()调用的返回值（已保存到中db）。

因此，代码的最后一部分应更改为：

更新

db.db.collectionNames(function (error, names) {
  if (error) {
    console.log('Error: '+ error);
  } else {
    console.log(names);
  };
});

我看不出有什么collectionNames办法Connection；看起来您必须遵循属性到本机连接对象中才能访问该对象（请参见上面的代码）。