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Intro-to-MongoDB

Repository for HackBU Demo on MongoDB (with Python & Flask)

About

MongoDB is Object-Oriented, simple, dynamic and scalable NoSQL database. It is based on the NoSQL document store model, in which data objects are stored as separate documents inside a collection instead of storing the data into columns and rows of a traditional relational database.

Setting Up

For this tutorial we will need to setup MongoDB locally on your machine. Click here to find an installation for your OS.

Familarity with Flask is helpful, but not essential.

Layout

  • MongoDB Installation
  • MongoDB Basics
  • Using MongoDB with Python3
  • Using MongoDB with Flask

Basics

Features

  • Persistent storage
  • Documents stored in BSON (binary JSON)
    • Mongo essentially uses JSON
  • JSON objects can be stored directly into a Mongo Database
  • Libraries with many popular languages (Python, Go, Javascript, etc.)

Concepts

Term Meaning
document database record, BSON object
Collections A Collection of documents or BSON objects
Queries Look up Cursors
Cursors Basically an index of a collection (Makes MongoDB really fast since it doesn't load the entire collection)

Using MongoDB with Python

There are many libraries for working with MongoDB in python. For our use, we will use pymongo.

Accessing a database

from pymongo import MongoClient

try:
    print("Connecting to Database...")
    client = MongoClient()
    db = client.HackBU
    print("Connected to db :)")
 except:
    print("Could not connect to db :(")

If you installed MongoDB properly and have a Mongo server running, this should print out Connected to db :).

Accessing a collection

try:
    users = db.users
    print("Connected to collection :)")
except:
    print("Could not connect to collection :(")

Finding a document

username = input("What is your username? Enter: ")

user = users.find_one({'username' : username})

if user is not None:
    print("Hello " + str(user['name']) + "!")
else:
    print("Could not find " + username + ".")

Inserting a document

username = input("Username: ")
name = input("Name: ")

new_user = {
    'username' : username,
    'name' : name
}

user = users.find_one({'username' : username})

if user is not None:
    print("User already exists!")
    return 
try:    
    users.insert_one(new_user).inserted_id
    print("Account created.")
except:
    print("Could not insert user.")

Deleting a document

username = input("What is your username? Enter: ")

user = users.find_one({'username' : username})

if user is None:
    print("User does not exist")
else:
    users.delete_one(user)
    user = users.find_one({'username' : username})
    if user is None:
        print("User deleted.")
    else:
        print("Could not delete user.")

Deleting a collection

try:
    users.drop()
    print("cleared users collection.")
except:
    print("Could not clear users collection.")

Iterating a collection

try:
    cursor = users.find({})
    for doc in cursor:
        print(doc)
except:
    print("Could not show users collection.")

Using MongoDB with Flask

Now we can take our previous code and use it with a flask app!

First import some libraries and create our Flask app

from flask import Flask
from flask import render_template
from flask import request
from pymongo import MongoClient

app = Flask(__name__)

Then setup our database:

try:
    print("Connecting to Database...")
    client = MongoClient()
    db = client.HackBU
    print("Connected to db :)")
except:
    print("Could not connect to db :(")

users = db.users

Next let's create our index route

@app.route("/")
def index():
    return render_template('index.html')

With index.html containing

<!doctype html>
Create account:<br>
<form action="/create">
  User Name:<br><input type="text" name="username">
  <br>
  Name:<br><input type="text" name="name">
  <br>
  <button>Create</button>
</form>

<br><br>

Login account:
<br>
<form action="/login">
  User Name:<br><input type="text" name="username">
  <br>
  <button>Login</button>
</form>

Next we can create our login route and create route

@app.route('/login', methods=['GET'])
def login():
    username = request.args.get('username', '')
    user = users.find_one({'username' : username})
    if user is None:
        return render_template('error.html', error="User does not exist.")
    print("User: " + str(user))
    return render_template('login.html', user=user)


@app.route('/create', methods=['GET'])
def create():
    username = request.args.get('username', '')
    name = request.args.get('name', '')
    new_user = {
        'username' : username,
        'name' : name
    }
    user = users.find_one({'username' : username})

    if user is not None:
        return render_template('error.html', error="User already exists!")

    try:    
        users.insert_one(new_user)
        print("Account created.")
        return render_template('login.html', user=new_user)
    except:
        return render_template('error.html', error="Could not insert user.")

Inside of login and create routes we use login.html and error.html

<!--login.html-->
<!doctype html>
{% if user %}
  <h1>Hello {{ user.name }}!</h1>
{% else %}
  <h1>User does not exist.</h1>
{% endif %}
<!--error.html-->
<!doctype html>
{% if error %}
  <h1>Error: {{ error }}</h1>
{% else %}
  <h1>404.</h1>
{% endif %}

The directory layout of our files is

/app.py
/templates
	/index.html
	/login.html
	/error.html

And then to run FLASK_APP=app.py flask run from the project directory.

And that's it! We now have a working flask app that can be used to create and login to accounts. Using Flask you can also setup sessions to keep a user logged in, along with some hashing libraries such as bcrypt to safely store users passwords.

Conclusion

MongoDB is a very powerful document database that may be used with a variety of languages. Python is one such language, and as shown above it is very easy to get a simple app up and running. By using Flask with pymongo, one can setup a simple app to create accounts and login.

Documentation