My Favorites List

The My Favorites Feature

Clicking the My Favorites link in the main navigation will take you to page which contains a list of Movies that you can want to revisit later.

When a logged in user hovers their mouse over a Movie on the website, a bookmark icon appears in the top left hand corner. Clicking this icon will either add or remove the Movie from the user’s Favorites list.

When adding a Movie to the list, a POST request it sent to the /api/favorites/{id} endpoint. When this happens, the following chain of events will occur:

Likewise, when it is clicked for a Movie that has already been favorited, a DELETE request is sent to the same URL, and the Movie is removed from the list.

When adding a Movie to a User’s Favorite list, a relationship is created between the User and Movie with the type HAS_FAVORITE.

Adding a Movie to My Favorites

For the first part of this challenge, modify the AddAsync() method to open a new database session, run the Cypher statement to create te relationship, close the session and return the movie details along with an additional favorite property.

// Open a new session
using var session = _driver.AsyncSession();
// Do something with the session...

MATCH (u:User {userId: $userId})
MATCH (m:Movie {tmdbId: $movieId})

MERGE (u)-[r:HAS_FAVORITE]->(m)
ON CREATE SET r.createdAt = datetime()

RETURN m {
    .*,
    favorite: true
} AS movie

var query = @"
    MATCH (u:User {userId: $userId})
    MATCH (m:Movie {tmdbId: $tmdbId})
    
    MERGE (u)-[r:HAS_FAVORITE]->(m)
    ON CREATE SET u.createdAt = datetime()

    RETURN m {
        .*,
        favorite: true
    } AS movie";
var cursor = await tx.RunAsync(query, new { userId, tmdbId });

if (!await cursor.FetchAsync())
{
    throw new NotFoundException($"Couldn't create a favorite relationship for User {userId} and Movie {tmdbId}");
}

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

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

    // Create HAS_FAVORITE relationship within a Write Transaction
    return await session.ExecuteWriteAsync(async tx =>
    {
        var query = @"
            MATCH (u:User {userId: $userId})
            MATCH (m:Movie {tmdbId: $tmdbId})
            
            MERGE (u)-[r:HAS_FAVORITE]->(m)
            ON CREATE SET u.createdAt = datetime()

            RETURN m {
                .*,
                favorite: true
            } AS movie";
        var cursor = await tx.RunAsync(query, new { userId, tmdbId });

        if (!await cursor.FetchAsync())
        {
            throw new NotFoundException($"Couldn't create a favorite relationship for User {userId} and Movie {tmdbId}");
        }

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

Removing a Movie from My Favorites

The second part of this challenge is to write the code to remove a movie from the My Favorites list.

The code for deleting the HAS_FAVORITE relationship will be similar, only the Cypher statement will change.

Instead of two separate MATCH clauses, we can instead attempt to find the pattern within a single clause. If the relationship (with an variable of r) exists, we will delete it and then return the movie information with favorite set to false.

MATCH (u:User {userId: $userId})-[r:HAS_FAVORITE]->(m:Movie {tmdbId: $movieId})
DELETE r

RETURN m {
    .*,
    favorite: false
} AS movie

Use the code from the AddAsync() method above to implement the remove() function. If you get stuck, you can reveal the completed method below.

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

    // Delete the HAS_FAVORITE relationship within a Write Transaction
    return await session.ExecuteWriteAsync(async tx =>
    {
        var query = @"
            MATCH (u:User {userId: $userId})-[r:HAS_FAVORITE]->(m:Movie {tmdbId: $tmdbId})
            DELETE r
            RETURN m {
              .*,
              favorite: false
            } AS movie";
        var cursor = await tx.RunAsync(query, new { userId, tmdbId });

        if (!await cursor.FetchAsync())
        {
            throw new NotFoundException($"Couldn't delete a favorite relationship for User {userId} and Movie {tmdbId}");
        }

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

Listing My Favorites

Finally, the AllAsync() method in the FavoriteService currently returns a hardcoded list of Movies from the fixture popular.json.

public async Task<Dictionary<string, object>[]> AllAsync(string userId, string sort = "title",
    Ordering order = Ordering.Asc, int limit = 6, int skip = 0)
{
    await using var session = _driver.AsyncSession();

    return await session.ExecuteReadAsync(async tx =>
    {
        var query = $@"
            MATCH (u:User {{userId: $userId}})-[r:HAS_FAVORITE]->(m:Movie)
            RETURN m {{
                .*,
                favorite: true
            }} AS movie
            ORDER BY m.{sort} {order.ToString("G").ToUpper()}
            SKIP $skip
            LIMIT $limit";

        var cursor = await tx.RunAsync(query, new {userId, skip, limit});
        var records = await cursor.ToListAsync();
        return records
            .Select(record => record["movie"].As<Dictionary<string, object>>())
            .ToArray();
    });
}

Update this method to return a paginated list of movies that the user has added to their My Favorites list.

MATCH (:User {userId: $userId})-[:HAS_FAVORITE]->(m)

RETURN m {
    .*,
    favorite: true
} AS movie

In the query the method we should also add dynamic sorting and pagination, with the string substitution for the sorting like we did in other places.

You have already written similar code a few times, so try to implement this one on your own. If you get stuck, you can view the full solution below.

public async Task<Dictionary<string, object>[]> AllAsync(string userId, string sort = "title",
    Ordering order = Ordering.Asc, int limit = 6, int skip = 0)
{
    await using var session = _driver.AsyncSession();

    return await session.ExecuteReadAsync(async tx =>
    {
        var query = $@"
            MATCH (u:User {{userId: $userId}})-[r:HAS_FAVORITE]->(m:Movie)
            RETURN m {{
                .*,
                favorite: true
            }} AS movie
            ORDER BY m.{sort} {order.ToString("G").ToUpper()}
            SKIP $skip
            LIMIT $limit";

        var cursor = await tx.RunAsync(query, new {userId, skip, limit});
        var records = await cursor.ToListAsync();
        return records
            .Select(record => record["movie"].As<Dictionary<string, object>>())
            .ToArray();
    });
}

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._07_FavoritesList"

The test file is located at Neoflix.Challenges/07-FavoritesList.cs.

git checkout 07-favorites-list