mongodb fails to connect even if i did exactly as the documentation

Question

I am making an app using nodejs and I am learning the mongodb, but I do it just like the docs. but the command prompt shows:

    events.js:141
      throw er; // Unhandled 'error' event
      ^

Error: Trying to open unclosed connection.
    at NativeConnection.Connection.open (C:\Users\html5col\Desktop\express\node_modules\mongoose\lib\connection.js:236:15)
    at Mongoose.connect (C:\Users\html5col\Desktop\express\node_modules\mongoose\lib\index.js:241:47)
    at Object.<anonymous> (C:\Users\html5col\Desktop\express\app.js:19:10)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Function.Module.runMain (module.js:441:10)
    at startup (node.js:139:18)
    at node.js:968:3

//my app.js file

    var url = 'mongodb://fran84:fran@ds013250.mlab.com:13250/ndeme';
    //ABOVE URL USING MLAB SERVICE

    var mongoose = require('mongoose');

    mongoose.connect(url);
    console.log('isonerror'); 
    var mydb = mongoose.connection;
    console.log('ismydb'); 


    mydb.on('error', console.error.bind(console, 'connection error:'));

    mydb.once('open', function() {
         // we're connected!
         console.log('Connected to MongoDB');

                var Schema = mongoose.Schema,
                    objectId = Schema.objectId;
                var postSchema = mongoose.Schema({//With Mongoose, everything is derived from a Schema. 
                    //id: objectId,//对象id
                    name: {type: String,default:20},
                    gender: {type: String,default:'male'},
                   // created_at:  Date     
                }, { timestamps });

                 //add "speak" functionality to our documents:  
                postSchema.methods.speak = function(){
                    var greeting = this.name
                        ? "His name is " + this.name
                        : "I do not have a nanme";
                    console.log(greeting);
                }                

                //The next step is compiling our schema into a Model
                var myModel = mongoose.model('try',postSchema);
                var instance = new myModel({name:'roger',gender:'female'});
                console.log(instance.name,instance.gender);
                instance.save(function(err,instance){
                    if(err){
                        return console.error(err);
                    }
                    instance.speak();

                });     


                //access all of the kitten documents through our myModel model.

                myModel.find(function(err,tries){
                    if(err){return console.error(err)}
                    console.log(tries);
                });
    });

MORE: ACCORDING DOCS:http://mongoosejs.com/docs/index.html

ADD 2: It seems that when I deletes the content of the mydb.once's callback function, it still shows the same problem.

Answer 1

The error is implying that you have already connected once in your application. Trying to connect again will throw the exception you're seeing.

Answer 2

You are trying to create another connection without closing the current one. you should use

createConnection() instead of connect().

It would look like:-

db = mongoose.createConnection(url);

Some sample linls for your help,

Why am I getting error "Trying to open unclosed connection."? Mongoose Trying to open unclosed connection