Pets Back End Show Route

Learning objective: By the end of this lesson, students will be able to create a new route to find a single pet by interacting with the database and sending a JSON response to the client.

READ - Show route

In this section, we will create a new route to find a single pet. This route will be a GET request to /pets/<pet_id>, returning a JSON response with a single pet from the database.

We will be following these specs when building the route:

• CRUD Action: READ
• Method: GET
• Path: /pets/<pet_id>
• Response: JSON
• Success Status Code: 200
• Success Response Body: A JSON object with the pet that matches the petId parameter.

• Error Status Code: 404

  500

• Error Response Body: A JSON object with an error message describing the error.

Let’s get started!

Defining the route

Inside app.py, create a new route to find a single pet. The method for this route is GET, and the path is /pets/:petId. Use the @app.route() decorator to create the route and pass in the path and the methods object:

# app.py

@app.route('/pets/<pet_id>', methods=['GET'])
def show_pet(pet_id):
    return f"Showing pet with id {pet_id}"

With the code above, we’ve created a testable route to ensure the pet_id parameter is working as intended. Send a request to localhost:5000/pets/1 in Postman and ensure the response message includes the pet_id.

Querying the database

We can now query the database for a pet using its unique identifier, pet_id. By implementing our query inside a try/except block, we can account for the following outcomes:

• Pet Found: In this scenario, we will return the pet’s data along with a status code of 200.
• Pet Not Found: If the resource cannot be located, we’ll return a 404 “Not Found” error message.
• Other Errors: If any unaccounted issues arise in the try, we’ll return a 500 status code along with an error message.

Add the following to app.py:

# app.py
@app.route('/pets/<pet_id>', methods=['GET'])
def show_pet(pet_id):
    try:
        connection = get_db_connection()
        cursor = connection.cursor(cursor_factory=psycopg2.extras.RealDictCursor)
        cursor.execute("SELECT * FROM pets WHERE id = %s", (pet_id,))
        pet = cursor.fetchone()
        if pet is None:
            connection.close()
            return "Pet Not Found", 404
        connection.close()
        return pet, 200
    except Exception as e:
        return str(e), 500

💡 Note the comma in the (pet_id,) argument provided to our execute method; this syntax ensures the value is treated as a tuple, which is necessary for parameterized queries to prevent SQL injection.

To test the route, open up Postman and send a GET request to http://localhost:5000/pets/1. You should receive a JSON response with the pet data as a single JSON object. You can also test the 404 failure scenario with a request to http://localhost:5000/pets/4978.