Mongoose random documents non sequential - node.js

Question

I have a node.js project and I need to get 8 random documents which are not sequential from my mongoDB database using Mongoose.
My Schema:
var mongoose = require('mongoose');
var random = require('mongoose-simple-random');
var schema = new mongoose.Schema({
title: String,
width:String,
height:String,
});
var Images = mongoose.model('Images', schema);
Images.count().exec(function (err, count) {
// Get a random entry
var random = Math.floor(Math.random() * count)
// Again query all users but only fetch one offset by our random #
Images.find({}).limit(8).skip(random).exec(
function (err, result) {
// Tada! random user
console.log(result)
//res.send(results);
})
})
module.exports = {
Images: Images
};
When calling the function in my route file (Main.js):
var Images = require('../models/images.js');
app.get('/homepage', function(req, res){
var rand = Math.floor(Math.random() * 10000);
Images.find({}).limit(8).skip(rand).exec(function(err, docs){
res.render('homepage', {images: docs});
});
});
How would I call the 'find' function in my model from my main.js route file?

Answer 1

You could use the following to get unique items with $sample but grouping by _id to remove possible duplicates in the random result :
db.images.aggregate([{
$sample: { size: 100 }
}, {
$group: {
_id: "$_id",
document: { $push: "$$ROOT" }
}
}, {
$limit: itemCount
}, {
$unwind: "$document"
}])
For the structure of your code, you could define a static method getRandomItems, storing your mongoose object in express app.db and calling the mongoose object from your router with req.app.db :
model.js
'use strict';
exports = module.exports = function(app, mongoose) {
var schema = new mongoose.Schema({
title: String,
width: String,
height: String,
});
schema.statics.getRandomItems = function(itemCount, cb) {
this.aggregate([{
$sample: { size: 100 }
}, {
$group: {
_id: "$_id",
document: { $push: "$$ROOT" }
}
}, {
$limit: itemCount
}, {
$unwind: "$document"
}], cb);
};
app.db.model('Images', schema);
};
app.js
'use strict';
var mongoose = require('mongoose'),
express = require('express');
var app = express();
app.db = mongoose.createConnection("mongodb://localhost/testDB");
// config data models
require('./models')(app, mongoose);
require('./routes')(app);
app.listen(8080, function() {
});
routes.js
'use strict';
exports = module.exports = function(app) {
// BboxAPI
app.get("/random", function(req, res) {
req.app.db.models.Images.getRandomItems(8, function(err, result) {
if (err) {
console.log(err);
res.status(500).json(err);
} else {
res.status(200).json(result);
}
});
});
};