How to do it...

The new directory layout would appear as follows:

flask_catalog/ 
    - run.py
    my_app/ 
        - __init__.py 
        catalog/ 
            - __init__.py 
            - views.py 
            - models.py 

First of all, start with modifying the application configuration file, that is, flask_catalog/my_app/__init__.py:

from flask import Flask 
from flask_sqlalchemy import SQLAlchemy 
 
app = Flask(__name__) 
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/test.db' 
db = SQLAlchemy(app) 
 
from my_app.catalog.views import catalog 
app.register_blueprint(catalog) 
 
db.create_all() 

The last statement in the file is db.create_all(), which tells the application to create all the tables in the database specified. So, as soon as the application runs, all the tables will be created if they are not already there.

Now is the time to create models that are placed in flask_catalog/my_app/catalog/models.py:

from my_app import db 
 
class Product(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    name = db.Column(db.String(255)) 
    price = db.Column(db.Float) 
 
    def __init__(self, name, price): 
        self.name = name 
        self.price = price 
 
    def __repr__(self): 
        return '<Product %d>' % self.id 

In this file, we have created a model named Product, which has three fields, namely id, name, and price. id is a self-generated field in the database, which will store the ID of the record and is the primary key. name is a field of the string type, and price is a field of the float type (which is coerced as decimal).

Now, add a new file for views, which is flask_catalog/my_app/catalog/views.py. In this file, we have multiple view methods, which control how we deal with the product model and the web application in general:

from flask import request, jsonify, Blueprint 
from my_app import db 
from my_app.catalog.models import Product 
 
catalog = Blueprint('catalog', __name__) 
 
@catalog.route('/') 
@catalog.route('/home') 
def home(): 
    return "Welcome to the Catalog Home." 

The preceding method handles how the home page or the application landing page looks or responds to users. You would most probably want to use a template for rendering this in your applications. We will cover this a bit later. Have a look at the following code:

@catalog.route('/product/<id>') 
def product(id): 
    product = Product.query.get_or_404(id) 
    return 'Product - %s, $%s' % (product.name, product.price) 

The preceding method controls the output to be shown when a user looks for a specific product using its ID. We filter for the product using the ID and then return its information if a product is found, or else abort with a 404 error. Consider the following code:

@catalog.route('/products') 
def products(): 
    products = Product.query.all() 
    res = {} 
    for product in products: 
        res[product.id] = { 
            'name': product.name, 
            'price': str(product.price) 
        } 
    return jsonify(res) 

The preceding method returns a list of all products in the database in JSON format. If no product is found, it aborts with a 404 error. Consider the following code:

@catalog.route('/product-create', methods=['POST',]) 
def create_product(): 
    name = request.form.get('name') 
    price = request.form.get('price') 
    product = Product(name, price) 
    db.session.add(product) 
    db.session.commit() 
    return 'Product created.' 

The preceding method controls the creation of a product in the database. We first get the information from a request and then create a Product instance from this information. Then, we add this Product instance to the database session and finally commit to save the record to the database.