There are two methods remaining in the MovieService that are currently returning hardcoded data.
-
FindByIdAsync() - should return information about a movie, including a list of actors, director, and genres.
-
GetSimilarMoviesAsync() - should return a list of similar movies, ordered by a score generated by Neoflix’s recommendation algorithm.
In this challenge, you will update these methods to query Neo4j.
First, let’s take a look at how these methods are used.
Movie Page
If you click on any movie, you’ll see that the API currently only returns information a limited set of movies from the fixtures in popular.json.
The page itself is populated by three API calls:
-
The details about the movie are loaded via the
api/movies/{id}endpoint. This endpoint gets its data from the FindByIdAsync() method. -
The similar movies list is loaded by a call to the
api/movies/{id}/similarendpoint, which gets its data from the GetSimilarMoviesAsync() method. -
The ratings on the right hand side of the page are loaded by a call to the
api/movies/{id}/ratingsendpoint. You will update this method in the next lesson.
FindByIdAsync()
Movie information is retrieved by the FindByIdAsync() method.
public async Task<Dictionary<string, object>> FindByIdAsync(string id, string userId = null)
{
// TODO: Find a movie by its ID
// MATCH (m:Movie {tmdbId: $id})
return await Task.FromResult(Fixtures.Goodfellas);
}Most of the important information is held as properties on the Movie node, but the payload should also return some additional information.
We can use a Cypher subquery and the count() aggregate function to get the number of ratings for the movie and use a Pattern Comprehension to get lists of actors, directors and genres.
As with the other movie methods in the MovieService, we should also provide a favorite value to represent whether the user has added this movie to their My Favorites list or not.
The following Cypher statement should be run within a read transaction:
MATCH (m:Movie {tmdbId: $id})
RETURN m {
.*,
actors: [ (a)-[r:ACTED_IN]->(m) | a { .*, role: r.role } ],
directors: [ (d)-[:DIRECTED]->(m) | d { .* } ],
genres: [ (m)-[:IN_GENRE]->(g) | g { .name }],
ratingCount: count{ (m)<-[:RATED]-() },
favorite: m.tmdbId IN $favorites
} AS movie
LIMIT 1Your Task
-
Modify the
FindByIdAsync()method to query Neo4j and return details for the requested movie. -
The returned object should include a list of actors, directors, genres, and a boolean flag to represent whether the movie exists on the current user’s My Favorites List.
-
If no records are returned, the method should throw a
NotFoundError(via thesingle()method on Result). -
Remember to close the session and use the
ToListAsync()function to convert the result object into native C# types.
Click to reveal the completed FindByIdAsync() method
public async Task<Dictionary<string, object>> FindByIdAsync(string id, string userId = null)
{
await using var session = _driver.AsyncSession();
var records = await session.ExecuteReadAsync(async tx =>
{
var favorites = await GetUserFavoritesAsync(tx, userId);
var query = @"
MATCH (m:Movie {tmdbId: $id})
RETURN m {
.*,actors: [ (a)-[r:ACTED_IN]->(m) | a { .*, role: r.role } ],
directors: [ (d)-[:DIRECTED]->(m) | d { .* } ],
genres: [ (m)-[:IN_GENRE]->(g) | g { .name }],
ratingCount: count { (m)<-[:RATED]-() },
favorite: m.tmdbId IN $favorites
} AS movie
LIMIT 1";
var cursor = await tx.RunAsync(query, new { favorites, id });
return await cursor.ToListAsync();
});
if (records.Count == 0)
{
throw new NotFoundException($"Could not find a Movie with tmdbId {id}");
}
return records.First()["movie"].As<Dictionary<string, object>>();
}GetSimilarMoviesAsync()
Similar movies are found using the GetSimilarMoviesAsync() method.
To provide a simple set of similar movies, the Cypher statement below uses the number of neighbors in common and their IMDB rating to generate a similarity score.
The following Cypher statement should be run within a read transaction:
MATCH (:Movie {tmdbId: $id})-[:IN_GENRE|ACTED_IN|DIRECTED]->()<-[:IN_GENRE|ACTED_IN|DIRECTED]-(m)
WHERE m.imdbRating IS NOT NULL
WITH m, count(*) AS inCommon
WITH m, inCommon, m.imdbRating * inCommon AS score
ORDER BY score DESC
SKIP $skip
LIMIT $limit
RETURN m {
.*,
score: score,
favorite: m.tmdbId IN $favorites
} AS movieYour Task
-
Modify the
GetSimilarMoviesAsync()method to query Neo4j and return a list of similar movies. -
The returned objects should include a list of actors, directors, genres, and a boolean flag to represent whether the movie exists on the current user’s My Favorites List.
-
Remember to close the session and use the
ToListAsync()functionresultto convert the values to native C# types.
Click here to reveal the completed GetSimilarMoviesAsync() method
public async Task<Dictionary<string, object>[]> GetSimilarMoviesAsync(string id, int limit, int skip, string userId = null)
{
await using var session = _driver.AsyncSession();
var records = await session.ExecuteReadAsync(async tx =>
{
var favorites = await GetUserFavoritesAsync(tx, userId);
var query = @"
MATCH (:Movie {tmdbId: $id})-[:IN_GENRE|ACTED_IN|DIRECTED]->()<-[:IN_GENRE|ACTED_IN|DIRECTED]-(m)
WHERE m.imdbRating IS NOT NULL
WITH m, count(*) AS inCommon
WITH m, inCommon, m.imdbRating * inCommon AS score
ORDER BY score DESC
SKIP $skip
LIMIT $limit
RETURN m {
.*,
score: score,
favorite: m.tmdbId IN $favorites
} AS movie";
var cursor = await tx.RunAsync(query, new { id, skip, limit, favorites });
return await cursor.ToListAsync();
});
return records
.Select(x => x["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._12_MovieDetails"The test file is located at Neoflix.Challenges/12-MovieDetails.cs.
Are you stuck? Click here for help
If you get stuck, you can see a working solution by checking out the 12-movie-details branch by running:
git checkout 12-movie-detailsYou may have to commit or stash your changes before checking out this branch. You can also click here to expand the Support pane.
Verifying the Test
What is the title of the most similar movie to Lock, Stock and Two Smoking Barrels?
As part of the test suite, the final test will log the title of the most similar movie to Lock, Stock & Two Smoking Barrels (tmdbId: 100).
Paste the title of the movie into the box below without quotes or whitespace and click Check Answer.
-
✓ Pulp Fiction
Hint
You can also find the answer by running the following Cypher statement:
MATCH (:Movie {tmdbId: '100'})-[:IN_GENRE|ACTED_IN|DIRECTED]->()<-[:IN_GENRE|ACTED_IN|DIRECTED]-(m)
WHERE m.imdbRating IS NOT NULL
WITH m, count(*) AS inCommon
WITH m, inCommon, m.imdbRating * inCommon AS score
RETURN m.title
ORDER BY score DESC
LIMIT 1Copy the answer without any quotes or whitespace.
Lesson Summary
In this Challenge, you modified the FindByIdAsync() and GetSimilarMoviesAsync() methods to return movie details from the Neo4j database.
In the next Challenge, you will complete the Movie page implementation by retrieving movie ratings from Neo4j.