When the user clicks a genre in the list, they are taken to a list of movies for that genre. This list is populated by an API request to /api/genres/[name], for example http://localhost:3000/api/genres/Comedy.
The find() method the the GenreService accepts one argument, the name of the genre, and should return the information about the genre, along with a count of movies and a poster image.
public Map<String,Object> find(String name) {
// TODO: Open a new session
// TODO: Get Genre information from the database
// TODO: Throw a 404 Error if the genre is not found
// TODO: Close the session
return genres.stream()
.filter(genre -> genre.get("name").equals(name))
.findFirst()
.orElseThrow(() -> new RuntimeException("Genre "+name+" not found"));
}In this challenge, you will modify the method to run the following Cypher statement in a read transaction:
MATCH (g:Genre {name: $name})<-[:IN_GENRE]-(m:Movie)
WHERE m.imdbRating IS NOT NULL AND m.poster IS NOT NULL AND g.name <> '(no genres listed)'
WITH g, m
ORDER BY m.imdbRating DESC
WITH g, head(collect(m)) AS movie
RETURN g {
.name,
movies: count { (g)<-[:IN_GENRE]-() },
poster: movie.poster
} AS genreWhat does this query do?
This query uses the MATCH clause for a Genre node with the name passed through with the function call as a parameter.
The query then finds the highest rated movie with a poster property and uses that image as the background to the card in the UI.
The size() function returns the number of incoming IN_GENRE relationships for each the Genre node.
Your Task
-
Modify the
find()method on theGenreServiceto call the Neo4j database and return details for a genre. -
The
namevariable should be passed to therun()call as a parameter. -
If no records or more than one record are found, a
NotFoundErrorshould be thrown by using thesingle()method onResult. -
Remember to close the session and use the
toMap()function to convert the genre values to native Java types.
Working Solution
Click here to view the completed find() method.
public Map<String,Object> find(String name) {
// Open a new Session, close automatically at the end
try (var session = driver.session()) {
// Get a list of Genres from the database
var query = """
MATCH (g:Genre {name: $name})<-[:IN_GENRE]-(m:Movie)
WHERE m.imdbRating IS NOT NULL
AND m.poster IS NOT NULL
AND g.name <> '(no genres listed)'
WITH g, m
ORDER BY m.imdbRating DESC
WITH g, head(collect(m)) AS movie
RETURN g {
link: '/genres/'+ g.name,
.name,
movies: count { (g)<-[:IN_GENRE]-() },
poster: movie.poster
} AS genre
""";
var genre = session.executeRead(
tx -> tx.run(query, Values.parameters("name", name))
// Throw a NoSuchRecordException if the genre is not found
.single().get("genre").asMap());
// Return results
return genre;
}
}Testing
To test that this functionality has been correctly implemented, run the following code in a new terminal session:
mvn test -Dtest=neoflix._10_GenreDetailsTestThe test file is located at src/test/java/neoflix/_10_GenreDetailsTest.java.
Are you stuck? Click here for help
If you get stuck, you can see a working solution by checking out the 10-genre-details branch by running:
git checkout 10-genre-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
How many movies are in the Action genre?
After the test has succeeded, the test suite will log the count of movies in the Action genre to the console.
Enter the number of movies below and click Check Answer.
-
✓ 1545
Hint
You can also find the answer by running the following Cypher statement:
MATCH (g:Genre {name: "Action"})
RETURN count { (g)<-[:IN_GENRE]-() }Lesson Summary
In this Challenge, you modified the find() method in the GenreService to retrieve genre information from Neo4j.
In the next Challenge, you will update multiple methods in the MovieService that return a paginated list of movies.