Express.js - How to Modify app.locals variables in routes

Question

I have a node.js project. The following code is part of my app.js file. I'm making a query from the database and storing the results in a global variabled called 'Cats'. I'm using this variable to display the categories on a sidebar of the site. I don't think its relevant but I am using Jade as templating engine.

var app = express()

var query = "SELECT * FROM findadoc.categories";
client.execute(query, [], function(err, results) {
  if(err) {
    res.status(404).send({meg: err});
  }
  else {
    app.locals.cats = results.rows;
  }
});

In one of the routes, I allow the user to add additional category to the database. What I need is for the 'apps.locals.cats' variable to get updated with the new set of categories. Is there anyway for me to modify this in my routes? I tried the following but it didn't work.

router.post('/add', function(req, res, next) {
    var cat_id = cassandra.types.uuid();
    var query = "INSERT INTO findadoc.categories(cat_id, name) VALUES (?,?)";
    client.execute(query, [cat_id, req.body.name], {prepare: true},   function(err, results) {
        if(err) {
            res.status(404).send({msg: err});
        } 
        else {
            cats = results.rows;
            req.flash('success', "Category Added");
            res.location('/doctors');
            res.redirect('/doctors');
        }
    });
});

Answer 1

In Express 4 You can access to app from req with req.app. See Request object API doc.

Locals are available in middleware via req.app.locals (see req.app)

In your middleware you could do it as this:

router.post('/add', function(req, res, next) {
    // do some cool stuff
    req.app.locals.cats = something;
    // more cool stuff
});