Adding The Favorite Flag

User Favorites

One way that we could find the user’s favorites would be to run a separate MATCH clause within the same query.

But as all of the routes that interact with the MovieService are used by both anonymous and logged in users, this could add unwanted complexity to the service.

Instead, it would be cleaner to execute two separate queries within the same transaction; one query to fetch a list of the user’s favorites, and another to retrieve a list of movies.

Fortunately, with only a few minor tweaks to the code, we can create a method that can be used to populate the favorite flag in the every other method in the MovieService.

Finding Favorites

Modify the GetUserFavoritesAsync() method to run the following query against the tx parameter.

MATCH (u:User {userId: $userId})-[:HAS_FAVORITE]->(m)
RETURN m.tmdbId AS id

private async Task<string[]> GetUserFavoritesAsync(IAsyncQueryRunner transaction, string userId)
{
    if (userId == null)
        return new string[] { };
    var query = @"
        MATCH (u:User {userId: $userId})-[:HAS_FAVORITE]->(m)
        RETURN m.tmdbId as id";
    var cursor = await transaction.RunAsync(query, new {userId});
    var records = await cursor.ToListAsync();

    return records.Select(x => x["id"].As<string>()).ToArray();
}

Adding the getUserFavorites call

Inside the AllAsync() method, we have used to just execute a single tx.RunAsync().

Instead of returning the results directly, you’ll need to add a call to GetUserFavorites(tx, userId) to get the list of favorite movies of the user, and then call the existing tx.RunAsync statement with the result of the GetUserFavorites function passed as an additional parameter $favorites.

Working Solution

If we take a look at the two versions of the AllAsync() method, not much has changed. The favorites array has been passed through as a parameter to the query, and the query now uses the Cypher IN clause to check if the ID is included in the array.

var cursor = await tx.RunAsync(@$"
    MATCH (m:Movie)
    WHERE m.{sort} IS NOT NULL       
    RETURN m {{
        .*,
        favorite: m.tmdbId IN $favorites
    }} AS movie
    ORDER BY m.{sort} {order.ToString("G").ToUpper()}
    SKIP $skip
    LIMIT $limit", new {skip, limit, favorites});

var cursor = await tx.RunAsync(@$"
    MATCH (m:Movie)
    WHERE m.{sort} IS NOT NULL
    RETURN m {{ .* }} AS movie
    ORDER BY m.{sort} {order.ToString("G").ToUpper()}
    SKIP $skip
    LIMIT $limit", new {skip, limit});