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 Save the Rating in a Write Transaction.

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 POST request to /api/account/ratings/{movieId} and the following will happen:

A rating is represented in the graph as 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 current user has given for the movie.

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

public async Task<Dictionary<string, object>> AddAsync(string userId, string tmdbId, int rating)
{
    // TODO: Convert the native integer into a Neo4j Integer
    // TODO: Save the rating in the database
    // TODO: Return movie details and a rating
    return await Task.FromResult(Fixtures.Goodfellas);
}

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

var updatedMovie = await session.ExecuteWriteAsync(async tx =>
{
    var cursor = await tx.RunAsync(@"
        MATCH (u:User {userId: $userId})
        MATCH (m:Movie {tmdbId: $tmdbId})
        
        MERGE (u)-[r:RATED]->(m)
        SET r.rating = $rating,
            r.timestamp = timestamp()
        
        RETURN m {
            .*,
            rating: r.rating
        } as movie", new {userId,
        tmdbId, rating});

    if (!await cursor.FetchAsync())
        return null;

    return cursor.Current["movie"].As<Dictionary<string, object>>();
});

if (updatedMovie == null)
    throw new NotFoundException($"Could not create rating for Movie: {tmdbId} for User: {userId}");

return updatedMovie;    

Working Solution

public async Task<Dictionary<string, object>> AddAsync(string userId, string tmdbId, int rating)
{
    await using var session = _driver.AsyncSession();

    var updatedMovie = await session.ExecuteWriteAsync(async tx =>
    {
        var cursor = await tx.RunAsync(@"
            MATCH (u:User {userId: $userId})
            MATCH (m:Movie {tmdbId: $tmdbId})
            
            MERGE (u)-[r:RATED]->(m)
            SET r.rating = $rating,
                r.timestamp = timestamp()
            
            RETURN m {
                .*,
                rating: r.rating
            } as movie", new {userId,
            tmdbId, rating});

        if (!await cursor.FetchAsync())
            return null;

        return cursor.Current["movie"].As<Dictionary<string, object>>();
    });

    if (updatedMovie == null)
        throw new NotFoundException($"Could not create rating for Movie: {tmdbId} for User: {userId}");

    return updatedMovie;    
}

Testing

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

dotnet test --logger "console;verbosity=detailed" --filter "Neoflix.Challenges._06_RatingMovies"

The test file is located at Neoflix.Challenges/06-RatingMovies.cs.

git checkout 06-rating-movies