Returned object is undefined, using dynamicHelpers - node.js

Question

I've created an external file that's handling the dynamic helpers, which includes a bunch of functions that I want to be able to use from all my views.
In on of the functions I'm running a query and fetch tags from the database, which I want to use in my layout.jade file (that all other views is using). In the console, all seems ok. The query returns the tags object, but by some strange reason I can't return the object to the view, which gives me an error message telling me that "tags" is undefined".
This is the code in my file dynamicHelpers.js:
exports.tags = function(req, res){
var environment = require('../environment');
var service = require('../service');
service.init(environment);
var model = service.useModel('tag');
var query = model.Tag.find({});
query.exec(function (err, tags) {
if (err) {
console.log(err);
// do something
}
console.log(tags);
return tags;
});
}
in layout.jade i'm getting the object in this way (this shows undefined):
p
#{tags}
What I actually want to do is to loop through all the tags with 'each'. So a follow-up issue would be if this is allowed and possible (if 'tags' were not undefined)?
ul.tags
each tag in #{tags}
a(href='/tag/' + tag._id.toHexString())
li.tag= tag.name
UPDATE:
I've tried #Linus G Thiel's solution (see below), but can't get it to work (res.tags gets undefined). With console.log(tags) in the middleware, it prints out the object. However, in the dynamicHelper function below it gets undefined. Seems like res.tags doesn't get passed to the dynamicHelper by some reason.
dynamicHelpers.js:
exports.tags = function(req, res) {
console.log(req.tags); <--- undefined
return req.tags;
};
configuration.js:
module.exports = function(app, express, next){
app.configure(function() {
// lots of more app.use functions (eg. express.cookieParser());)
// ...
app.use(function(req, res, next) {
var environment = require('./environment');
var service = require('./service');
service.init(environment);
var model = service.useModel('tag');
var query = model.Tag.find({});
query.exec(function (err, tags) {
if (err) {
return next(err);
}
req.tags = tags;
next();
console.log(req.tags); <--- works fine
});
});
});
};

Answer 1

As #Exploit says in his comment, your tags function makes an async call to query.exec, which will finish after your tags function has returned. Express' helpers and dynamicHelpers can't be async, so you need to refactor this somehow. One way would be to put it on req in an earlier middleware or route, and then have a simple dynamicHelper which returns that:
dynamicHelpers.js:
exports.tags = function(req, res) {
return req.tags;
};
Middleware (you might not want to do this for all routes, you could look into e.g. Route specific middleware or Route param pre-conditions):
app.use(function(req, res, next) {
var environment = require('../environment');
var service = require('../service');
service.init(environment);
var model = service.useModel('tag');
var query = model.Tag.find({});
query.exec(function (err, tags) {
if (err) {
return next(err);
}
req.tags = tags;
next();
});
});

Answer 2

It's kinda dirty but you can do this to wait for tags to be set. The solution Linus G Thiel provided is better though because this will block your application.
tags: function(req, res) {
var environment = require('../environment');
var service = require('../service');
service.init(environment);
var model = service.useModel('tag');
var query = model.Tag.find({});
var _tags = false;
query.exec(function (err, tags) {
if (err) {
console.log(err);
// do something
}
console.log(tags);
_tags = tags;
});
while(_tags == false);
return _tags;
}
Have you tried it like this?
exports = function(app) {
app.dynamicHelpers({
tags: function(req, res) {
var environment = require('../environment');
var service = require('../service');
service.init(environment);
var model = service.useModel('tag');
var query = model.Tag.find({});
query.exec(function (err, tags) {
if (err) {
console.log(err);
// do something
}
console.log(tags);
return tags;
});
}
});
}
require("helpers")(app);

Answer 3

You need to defined the middleware before the other routes
module.exports = function(app, express, next){
app.configure(function() {
app.use(function(req, res, next) {
var environment = require('./environment');
var service = require('./service');
service.init(environment);
var model = service.useModel('tag');
var query = model.Tag.find({});
query.exec(function (err, tags) {
if (err) {
return next(err);
}
req.tags = tags;
next();
console.log(req.tags); <--- works fine
});
});
// lots of more app.use functions (eg. express.cookieParser());)
// ...
});
};