mongoose find next object

Question

I am creating a photography website and eventually I would like to add the functionality for the user to see the next photo in the database. I am new to web development and therefore want to proceed step by step, so for now it would be enough if the id of the next photo would be displayed in the console. This is the code I use right now:

var getPhoto = require("../public/modules/getPhoto")

router.get("/:id/next", function(req, res){
    getPhoto.next();
    res.redirect("/");
})

and

var Photo = require("../../models/photo");
var exports = module.exports = {};

exports.next = function(callback){
    console.log(Photo.find({}).sort({_id: 1 }).limit(1)._id);
}

However, this only returns undefined.

I read here that I need to use callbacks, but I don't know how to implement it, even with the code given in the example in the link.

How can I print the id of the next photo to console?

Edit My code now looks like this:

// NEXT PHOTO - shows next photo 
router.get("/:id/next", function(req, res){
    Photo.find({}).sort({ _id: 1 }).limit(1).then(function(docs){ 
        console.log(docs[0]._id)
        res.redirect("/photos/" + docs[0]._id)
    })
})

// PREVIOUS PHOTO - shows previous photo 
router.get("/:id/previous", function(req, res){
    Photo.find({}).sort({ _id: -1 }).limit(1).then(function(docs){ 
        console.log(docs[0]._id)
        res.redirect("/photos/" + docs[0]._id)
    })
})

However, this only gives me the first or last item in the database. According to this link I have to substitute { _id: -1 } for {_id: {$gt: curId}}. I am not using jQuery, so how can I rewrite this?

You don't *need* to use callbacks, you can also make use of the Promise being returned from Mongoose.... but if you aren't familiar with either of those concepts then personally I'd advise you start with learning the basics of Node. Also, there are examples in the [mongoose docs](https://mongoosejs.com/docs/promises.html). — James, Nov 22 '18 at 20:02
Don't believe what you read in the first post you find. From 2016 if the answer had any credibilty then it would have significantly more votes than 1. As the comment ays *"read the documentation **first**"*. You can ask questions and read others answers once you see what the documentation has to say. And it says `Photo.find({}).sort({ _id: 1 }).limit(1).then( docs => console.log(docs[0]._id) )`. As does the other main point of the more cannonical and highly voted answer as now linked. — Neil Lunn, Nov 23 '18 at 03:05
Or `Photo.findOne({}).sort({ _id: 1 }).then( doc => console.log(doc) )` for that matter — Neil Lunn, Nov 23 '18 at 03:09

score 0 · Answer 1 · answered Nov 23 '18 at 00:30

You need to understand callbacks and Promises. But for your answer, you can take advantage of mongoose exec like this:

exports.next = function() {
    return new Promise((resolve, reject) => {
        Photo.find({}).sort({_id: 1}).limit(1).exec(function(err, photos) {
            if (err) {
                reject(err);
            }
            console.log('received: ', photos);
            resolve();
        }
    }
}

Then in your router you should have:

getPhoto.next().then(function() {
    res.redirect('/');
});

This is literally the basic usage of Promises in JS. There are lots of articles about usage of Promises and you can easily find them, and you can go to mongoose official page on how to query to mongo and get the results.

From above comment *"you can also make use of the Promise being returned from Mongoose.."* - And [when you look](https://mongoosejs.com/docs/api.html#model_Model.find), you will see that the API allows a Promise to be returned without wrapping in a Promise yourself. So the comment that was there 4 hours before you answered was valid for you to read as well. — Neil Lunn, Nov 23 '18 at 03:01

mongoose find next object

1 Answers1