Rating Movies

The Request Lifecycle

Before we start, let’s take a look at the request lifecycle when saving a review. If you prefer, you can skip to Saving a Rating.

On every Movie page, the user is invited to rate a movie on scale of 1 to 5. The form pictured to the right gives the user the ability to select a rating between 1 and 5 and click submit to save the rating.

When the form is submitted, the website sends a request to /api/account/ratings/{movieId} and the following will happen:

A rating is represented in the graph a relationship going from a :User to a :Movie node with the type :RATED. The relationship has two properties; the rating (an integer) and a timestamp to represent when the relationship was created.

After the data is saved, the UI expects the movie details to be returned, with an additional property called rating, which will be the rating that the user has given for the movie.

Let’s take a look at the existing method in the RatingDAO.

def add(self, user_id, movie_id, rating):
    # TODO: Create function to save the rating in the database
    # TODO: Call the function within a write transaction
    # TODO: Return movie details along with a rating

    return {
        **goodfellas,
        "rating": rating
    }

Your challenge is to replace the TODO comments in this method with working code.

Saving a Rating

Complete the following steps to complete the challenge:

# Create function to save the rating in the database
def create_rating(tx, user_id, movie_id, rating):
    return tx.run("""
    MATCH (u:User {userId: $user_id})
    MATCH (m:Movie {tmdbId: $movie_id})
    MERGE (u)-[r:RATED]->(m)
    SET r.rating = $rating,
        r.timestamp = timestamp()
    RETURN m {
        .*,
        rating: r.rating
    } AS movie
    """, user_id=user_id, movie_id=movie_id, rating=rating).single()

with self.driver.session() as session:
    record = session.execute_write(create_rating, user_id=user_id, movie_id=movie_id, rating=rating)

if record is None:
    raise NotFoundException()

return record["movie"]

Working Solution

def add(self, user_id, movie_id, rating):
    # Create function to save the rating in the database
    def create_rating(tx, user_id, movie_id, rating):
        return tx.run("""
        MATCH (u:User {userId: $user_id})
        MATCH (m:Movie {tmdbId: $movie_id})
        MERGE (u)-[r:RATED]->(m)
        SET r.rating = $rating,
            r.timestamp = timestamp()
        RETURN m {
            .*,
            rating: r.rating
        } AS movie
        """, user_id=user_id, movie_id=movie_id, rating=rating).single()

    with self.driver.session() as session:
        record = session.execute_write(create_rating, user_id=user_id, movie_id=movie_id, rating=rating)

        if record is None:
            raise NotFoundException()

        return record["movie"]

Testing

To test that this functionality has been correctly implemented, run the following code in a new terminal session:

pytest tests/06_rating_movies__test.py

The test file is located at tests/06_rating_movies__test.py.

git checkout 06-rating-movies