How can I "cache" a mongoDB/Mongoose result to be used in my Express.js views and routes

Question

What I'm trying to achieve is some sort of way to cache results of a mongoDB/Mongoose query that I can use in my views and routes. I'd need to be able to update this cache whenever a new document is added to the collection. I'm not sure if this is possible and if it is then how to do it, due to how the functions are asynchronous

This is currently what I have for storing the galleries, however this is executed with every request.

app.use(function(req, res, next) {
  Gallery.find(function(err, galleries) {
    if (err) throw err;  
      res.locals.navGalleries = galleries;
      next();
  });
});

This is used to get gallery names, which are then displayed in the navigation bar from a dynamically generated gallery. The gallery model is setup with just a name of the gallery and a slug

and this is part of my EJS view inside of my navigation which stores the values in a dropdown menu.

<% navGalleries.forEach(function(gallery) { %>
  <li>
    <a href='/media/<%= gallery.slug %>'><%= gallery.name %></a>
  </li>
<% }) %>

The website I'm working on is expected to get hundreds of thousands of concurrent users, so I don't want to have to query the database for every single request if not needed, and just update it whenever a new gallery is created.

Answer 1

Take a look at cachegoose. It will allow you to cache any query you want and invalidate that cache entry each time a new gallery is created.

You will need something like this:

const mongoose = require('mongoose');
const cachegoose = require('cachegoose');

cachegoose(mongoose); // You can specify some options here to use Redis instead of in-memory cache

app.get(function(req, res, next) {
    ...

    Gallery
        .find()
        .cache(0, 'GALLERY-CACHE-KEY')
        .exec(function(err, galleries) {
            if (err) throw err;  

            res.locals.navGalleries = galleries;

            next();
    });

    ...
});

app.post(function(req, res, next) {
    ...

    new Gallery(req.body).save(function (err) {
        if (err) throw err;

        // Invalidate the cache as new data has been added:
        cachegoose.clearCache('GALLERY-CACHE-KEY');
    });

    ...
});

Although you could do something simpler caching the results manually in a variable and invalidating that cache when new galleries are added, I would advise you to take a look at that package instead.