mLab database not accessible from heroku hosted MEAN app - node.js

Question

I have hosted my MEAN app on heroku using mlab to provide the mongodb database I need.
In my app, I connect to the database using :
mongoose.connect(process.env.MONGODB_URI);
In my app, I declare my model :
mongoose.model('Course', CourseSchema);
If I understand correctly, mongoose will look for a collection named Courses.
I have imported a collection into mlab using :
mongoimport -h <XXX> -d <XXXXX> -c Courses -u <XXXX> -p <XXXX> --file <XXXXX> --jsonArray
It worked, message : imported 350 documents
And yet, my app doesn't show any data while it works locally.
What could be happenning ? I'm a total beginner and don't really know where to start :)
EDIT :
In my app, I have a get request on the database triggered by the route : /courses
Here is what I get in the logs regarding that get request :
2016-06-09T17:33:57.000199+00:00 app[web.1]: GET /courses 304 2.473 ms - -
2016-06-09T17:34:34.739488+00:00 heroku[router]: at=info method=GET path="/" host=c
mtproto.herokuapp.com request_id=dbdef76d-78b2-4d4c-b509-a18c6194cc18 fwd="87.91.22
.213" dyno=web.1 connect=0ms service=2ms status=304 bytes=147
2016-06-09T17:34:34.734195+00:00 app[web.1]: GET / 304 1.106 ms - -
I'm really confused, I just tried my app locally with my local database (on localhost) without any issue.
Then I ran it locally using my mongolab uri to connect to the database managed by mlab. The connection worked (response : 200) but had no data in my app. I then proceded to use curl http://localhost:3000/courses and got an empty array in response.
I dont think the problem comes from the code of my get request since it works when I connect to my localhost database. Code of my get request :
router.get('/courses', function(req, res, next) {
Course.find(function(err, courses){
if(err){ return next(err); }
res.json(courses);
}).select({ "name": 1, "_id": 1, 'code': 1, 'courseContentGrade': 1, 'courseTeachingGrade': 1, 'courseAverage': 1});
});
It also looks like I do connect succesfully to the mlab database since I get a 200 code response.I get a 304 if I use a post request though.
here is what the data in db looks like :
[{
"_id": {
"$oid": "5759ddbfe71976730e6df425"
},
"code": "XXXXXX ",
"name": "Negotiation",
"courseContentGrade": "3.0",
"courseTeachingGrade": "8.0",
"courseAverage": "5.5",
"reviews": [
{
"name": "Advanced Negotiation Workshop",
"professor": "Aenean sed",
"contentReview": "Lorem ipsum dolor sit amet, consectetur adipiscing",
"teachingReview": "In in ipsum odio. Nulla sodales nulla vel vulputate lobortis. Curabitur ut.",
"contentGrade": 3,
"teachingGrade": 8,
"average": "5,5",
"trimester": "T3",
"day": "Semaine bloquée",
"time": "Semaine bloquée",
"round": "1er tour / 1st round",
"bet": 21,
"year": "2014/2015",
"upvotes": 0,
"author": "Piranha"
}
]
},
{
"_id": {
"$oid": "5759ddbfe71976730e6df42a"
},
"code": "XXXXXXXX",
"name": "Germany",
"courseContentGrade": null,
"courseTeachingGrade": null,
"courseAverage": null,
"reviews": []
}]
Any other hint on what I should be checking ?

Answer 1

Problem solved !
Mongo doesn't like capital letters, I renamed my collection with only lower case letters and everything is now working perfectly.
No idea why it was working on my computer and not on heroku though...

Answer 2

While deploying your apps, it's a good practice to keep API keys and auth related variables out of codebase. This way your secrets are safe, even when codebase is shared. These secrets can be applied to the run time using process.env object which can store all such environmental variables.
For heroku based deployments you can set your environment variables by using following command:
heroku config:set GITHUB_USERNAME=vikramtiwari
More details: https://devcenter.heroku.com/articles/config-vars
Once these variables are set your program can make use of it during run time. In your case, your MEAN app is trying to find those values, but couldn't get them, hence no data being displayed. Check your logs (heroku logs) to confirm that app is not connected to MongoDB.