Working with Flask, MongoDB and CharJS for nice data visualization with python

Working with Flask, MongoDB and CharJS for nice data visualization with python

2020, Feb 20    

In this post i want to share some major tips to visualize data using python and mongodb. For the visualization part we use ChartJS although any other library available might be also suitable. For this post we will use an existing dataset so the main focus will be: Inititalize your flask app, database connection, data query, passing the data to template engine and use the data to generate charts.

Flask app

Flask is very easy, light and small python framework to build web servers. I enjoy using it a lot because of its flexibility. To start using it (asuming you have already installed the package) you only need following code snippet:

    from flask import Flask, render_template, url_for

    app = Flask(__name__)

    def index():
        return render_template('index.html')

    if __name__ == "__main__":'',debug=True)

Voilà, now you already have a web server running on your

MongoDB Connection

In my case, my data is saved in a MongoDB database in an AWS EC2 linux instance manually created. So to connect to the database we need to authenticate in the Ec2 instance before. Usually these connections are secured with SSH protocol. So in python we need to install the library sshtunnel and use the package SSHTunnelForwarder.

To create the connection we need to fill following data:

def connectSSH():
    server = SSHTunnelForwarder(
    (os.getenv("MONGO_HOST"), 5552),
    remote_bind_address=(os.getenv("MONGO_LOCALHOST"), 27017),
    local_bind_address=(os.getenv("MONGO_LOCALHOST"), 27017),
    return connectionSSH

MONGO_HOST is the ip address of the EC2 instance MONGO_SSH_USER is the user of the EC2 instance, depending on the type of AMI used it could be: ec2-user, ubuntu, root, admin etc. MONGO_SSH_PRIVATE_KEY is the path where your PEM key is located in case you use this method to connect to the instance. MONGO_LOCALHOST is the address where the MongoDB is installed, if you follow normal procedure this would be the localhost address (

The previous code returns connectionSSH which shoould be started like this (assuming it is saved in a variable called server):


Once you finish your work on the instance, you should manually close the connection to avoid problems (the library usually fails when we kept the connection open):


So now you have tested the SSH connection we can connect to the Mongo database.

    client = MongoClient(os.getenv("MONGO_LOCALHOST"), 27017)

At this point you can perform any query on the Mongo database with the variable client.

MongoDB Query

To perform queries on MongoDB with python we use the library PyMongo which is probably the most popular and used library for MongoDB.

To start performing query we need to define the DB where the query will be executed. In the following example we select ‘company’ as the DB

    db = client['company']

On the db variable we can perform the MongoDB queries, let’s do with some examples:

    usersData = db.users.find({"type": 0}, {'_id': 1, 'email': 1, 'created_at': 1})

Previous query is executed in the collection users, the first ‘{}’ is used to add some filters, in this case we are querying all the users where the field type is 0. The second ‘{}’ is to define what fields to get from the query, sometimes the collection has too many fields and we only need few, so we use this second array to define which fields to obtain.

The result are saved as cursor object in usersData, that means that you need to iterate over the cursor with a loop similar to this:

    total_users = 0
    recent24h_users = 0
    recentWeek_users = 0
    for item in usersData:
        total_users = total_users + 1
        if item['created_at'] > ( - timedelta(hours=24)):      
            recent24h_users = recent24h_users + 1
        if item['created_at'] > ( - timedelta(hours=168)): 
            recentWeek_users = recentWeek_users + 1
    getKPIUsers = {
            'totalUsers': total_users,
            'recent24hUsers': recent24h_users,
            'recentWeekusers': recentWeek_users

So in previous code snipet we are counting the total of users registered in the collection, the total users registered in the past 24 hours and 7 days and storing the data in a dict object.

Passing MongoDB data to HTML templates and graph it

Now that we have our data collected from MongoDB we need to pass it to our view to chart. For this case we use a method provided by flask called render_template

    return render_template('dashboard.html', KPIUsers=getKPIUsers)

Previous code loads the ‘dashboard.html’ file and send a the data in a variable called *KPIUsers.

In the HTML file we have following code to generate the chart:

    <!-- Chart.js is loaded here -->
    <link rel="stylesheet" href="">
    <script src=""></script>
        <canvas id="users" width="150" height="50"></canvas>
        var ctxUsers = document.getElementById('users').getContext('2d');
        var users = new Chart(ctxUsers, {
            type: 'bar',
            data: {
                labels: ['Total', 'Recent 24H', 'Recent Week'],
                datasets: [{
                    label: 'Registro de usuarios',
                    data: [{\{KPIUsers['totalUsers']}}, {\{KPIUsers['recent24hUsers']}}, {\{KPIUsers['recentWeekusers']}}], /* Remove the backslashes \ */
                    backgroundColor: 'rgba(63, 191, 127, 0.2)',
                    borderColor: 'rgba(63, 191, 127, 1)',
                    borderWidth: 1

Notice that the arrangement of the labels and data must be equal to match each KPI with corresponding label. You have tons of options to customize your chart and the documentation is very easy to understand.

Hope this post is useful for you, if you have any suggestion/comment/question drop a comment below.

Live long and code! :v::v: