questions when using mongoose in Node.js

Question

I am learning Node.js using Beginning Node.js written by Mr. Basarat Syed.

I have come across the following mongoose code snippet. My question is about the last three lines with db.close() and how does the collection tanks come up without any statement about tanks.

var mongoose = require('mongoose');

var tankSchema = new mongoose.Schema({name: 'string', size: 'string'});
tankSchema.methods.print = function () {
    console.log('I am', this.name, 'the', this.size)
};

var Tank = mongoose.model('Tank', tankSchema);

mongoose.connect('mongodb://127.0.0.1:27017/demo');
var db = mongoose.connection;
db.once('open', function callback() {
    console.log('connected!');

    var tony = new Tank({
        name: 'tony',
        size: 'small'
    });
    tony.print();

    tony.save(function (err) {
        if (err) throw err;
        Tank.findOne({name: 'tony'}).exec(function (err, tank) {
            tank.print();

            //======Here are the three lines=======
            db.collection('tanks').drop(function(){db.close();});// The one in the book.
            //db.close();
            //db.collection('t').drop(function(){db.close();});
        });
    });
});

My question is what is the difference among the last three lines? Where did the collection('tanks') come from? Why not just use db.close() like the second one? It seems that I could use any legal string as the argument of collection on for example the third sentence 't'. How could this happen?

I don't get it. Can you please frame your questions more appropriately? What exactly is your question. — Gandalf the White
– Gandalf the White, Commented Jan 11, 2016 at 11:15
@GandalftheWhite Sorry for my bad frame about the questions. I have made some edit and not sure if it is clear now. Although X.L.Ant has made the picture much clear now. :) — krave
– krave, Commented Jan 11, 2016 at 15:32

xlecoustillier · Accepted Answer · 2016-01-11 15:40:02Z

2

When you save an instance of the Tank model, mongoose simply infers the collection name to tanks (lowercase Tank + the s suffix), and creates the collection if needed (i.e. if it doesn't already exist), unless you explicitly tell it another name to use, like this:

var tankSchema = new mongoose.Schema({name: 'string', size: 'string'}, { collection: 'myTanks' });

The following statement drops the tanks collection you created by saving a tank using the Tank model, and then closes the connection

db.collection('tanks').drop(function(){db.close();});

This statement only closes the connection, without doing anything else

db.close();

This one drop the collection t (which I guess doesn't exist in your case), and then again closes the connection

db.collection('t').drop(function(){db.close();});

edited Jan 11, 2016 at 15:40

answered Jan 11, 2016 at 11:18

xlecoustillier

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2 Comments

krave Over a year ago

So the collection tanks has already be created by mongoose implicitly according to the Model name - Tank. Thank you very much! Much clear now. :)

xlecoustillier Over a year ago

Exactly. The collection is created when you try to save the first object, if it doesn't already exists. Edited to clarify this point.

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