Sample Flask App

Problem

Write a sample backend application for an online marketplace. The following is a view on the products available on the site:

Product ID	Name	Price	Currency
5	Chocolate	2.50	USD
6	Salad bio	1.90	USD
7	Fresh Seafood	32.45	USD

Implement a RESTful API that provides endpoints for:

• listing all the available products, with their name and price in JSON format (HTTP method GET)
• creating a new product with the information provided (HTTP method POST)
• listing all the information related to a specific product in JSON format (HTTP method GET)
• Update the information related to a specific product (HTTP method PUT)
• Delete a specific product (HTTP method DELETE)

Ensure that coherent return values are returned both in case of success and in case of failure: e.g. the web service should return a 404 HTTP error when asked for the information of a non-existing product.

Implementation requirements

To implement the web service, use Python3 together with the Flask framework. You're free to choose the database technology of your preference along with any Flask extension publicly available. Be sure to include a requirements.txt file in your solution.

Solution

The solution has been implemented in python3.5 and it's guaranteed to work on that python version. The project has been organized into two main folders. The core folder contains both the data model (models.py) and the implementation of the API (api.py) while the folder tests contains the unit tests related to the endpoints exposed by the API. Finally the main of the program is located at the root level of the project (main_app.py) along with the default configuration file config.py.

Execution environment

It's strongly recommended to set up a virtual environment, install the requirements, and run the solution (both the main application and the tests) within the virtualenv.

By using virtualenvwrapper this can be simply done with:

mkvirtualenv -a /path/to/this/project -p /path/to/your/python3 -r /path/to/this/project/requirements.txt sample-flask-app

You can even install the requirements at a later time by doing:

pip3 install -r /path/to/this/project/requirements.txt

Running the program

Since the program connects to a postgreSQL database, in order to be able to connect to your own database you need to do just a few more set up operations. In config.py, defaults are provided for the development, testing, staging and productions environments. Switching between different environments is implemented via the SAMPLE_FLASK_APP_ENV environment variable and the triggering values are:

• dev to refer to the development environment
• test to refer to the testing environment
• stage to refer to the staging environment
• prod to refer to the production environment

It's possible to overwrite defaults by providing an additional custom file with settings in the SAMPLE_FLASK_APP_ENV environment variable.

Let's say you want to execute this program in the dev mode:

1. Create a dev_config.py under the .config folder at the root level of the project.

2. Fill the dev_config.py with the settings you want to overwrite. For example, in my case this file contains:

    SQLALCHEMY_DATABASE_URI = 'postgresql://gioiaballin@localhost:5432/products'
   

3. Export the environment variable before running the app:

   export SAMPLE_FLASK_APP_ENV="dev"
   export SAMPLE_FLASK_APP_SETTINGS="./.config/dev_config.py"
   

4. Run the application from the root level of the project with:

   python3 main_app.py
   

Aside note: remember to add this project to your PYTHONPATH in order to avoid problems with import statements.

Running the tests

In order to run the tests you still need to set the SAMPLE_FLASK_APP_SETTINGS in order to feed the tests with the right URL of the testing database. Setting the SAMPLE_FLASK_APP_ENV is not needed because the tests already refers to the testing default configuration.

If you want to execute the tests:

1. Create a test_config.py under the .config folder at the root level of the project.

2. Fill the test_config.py with the settings you want to overwrite. For example, in my case this file contains:

    SQLALCHEMY_DATABASE_URI = 'postgresql://gioiaballin@localhost:5432/test_products'
   

3. Run the tests from the root level of the project with:

   python -m unittest tests/test_api_endpoints.py