Flask Part II

Now that we're ready to make non-simple requests, we'll learn about and practice making complex GET requests and additional requests (POST, PATCH, and DELETE), using CORS and basic error handling.

Flask Route Decorator

You've already seen the @app.route decorator used in its most basic form like so:

@app.route('/hello')
def get_greeting():
    return jsonify({'message':'Hello, World!'})

In addition, the @app.route decorator can handle Variable Rules and multiple HTTP methods

Variable Rules

In our endpoint naming scheme we follow collection/item/collection . In order to handle that variable item. In order to handle that variability in Flask, you add a <variable_name> within the path argument of the @app.route decorator, which is then passed to the function as a keyword argument variable_name.

You can also specify the type of the argument by using <converter:variable_name> syntax.

@app.route('/entrees/<int:entree_id>')
def retrieve_entree(entree_id):
    return 'Entree %d' % entree_id

HTTP Methods

By default, the @app.route decorator answers only get requests. In order to enable more requests types, pass the method parameter to the decorate including a list of string methods.

@app.route('/hello', methods=['GET', 'POST'])
def greeting():
    if request.method == 'POST':
        return create_greeting()
    else:
        return send_greeting()

OPTIONS requests are automatically implemented and HEAD is also automatically implemented if GET is present.

Pagination in Flask

When handling large collections of data, attempting to serialize and send all of that data to the frontend will slow down the response and rendering to the client.

A common way to handle this issue is to paginate the data you're sending, and send it in chunks instead. Similar to variables discussed above, flask can handle request arguments to get additional request conditions such as page or search terms.

Query Parameters

The below examples show the format of query parameters. When writing query parameters convention dictates that:

• A question mark precedes the query parameters
• Parameters are in key=value pairs with an equal sign in between the key and value
• Sets of parameters are separated by an ampersand

www.example.com/entrees?page=1

www.example.com/entrees?page=1&allergens=peanut

Request Arguments

In flask, when a request is received with query params the route in the @app.route decorator remains the same and the request object arguments contains the parameter. You access it as shown below. request.args is a Python dictionary so we use the get method to access the value and provide a default value, in this case 1.

@app.route('/entrees', methods=['GET'])
  def get_entrees():
    page = request.args.get('page', 1, type=int)

QUIZ QUESTION: :

Match the sample app.route decorators with the concepts they demonstrate.

ANSWER CHOICES:

@app.route('/students')

@app.route('/students/<int:student_id>')

@app.route('/students',  methods=['GET', 'POST'])

@app.route('/students',  methods=['GET', 'POST'])

@app.route('/students/<int:student_id>')

@app.route('/students')