If you click on the Genres link in the main navigation, you will be taken to a list of Genres.
This list is populated by the API route at http://localhost:3000/api/genres, with the list being produced by the all() method within the GenreService.
public List<Map<String, Object>> all() {
// TODO: Open a new session
// TODO: Get a list of Genres from the database
// TODO: Close the session
return genres;
}In this challenge, you will modify the method to run the following Cypher statement in a read transaction:
MATCH (g:Genre)
WHERE g.name <> '(no genres listed)'
CALL {
WITH g
MATCH (g)<-[:IN_GENRE]-(m:Movie)
WHERE m.imdbRating IS NOT NULL AND m.poster IS NOT NULL
RETURN m.poster AS poster
ORDER BY m.imdbRating DESC LIMIT 1
}
RETURN g {
.*,
movies: count { (g)<-[:IN_GENRE]-(:Movie) },
poster: poster
}
ORDER BY g.name ASCYour Task
-
Modify the
all()method on theGenreServiceto query Neo4j and return a list of properties ordered by genre name. -
Each genre should have a name, the number of movies listed in that genre (
movies), and a poster image (from the most popular movie in that genre). -
Remember to close the session and use the
toMap()functionresult.listto convert the values to native Java types.
Working Solution
Click here to view the completed all() method.
public List<Map<String, Object>> all() {
// 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)
WHERE g.name <> '(no genres listed)'
CALL {
WITH g
MATCH (g)<-[:IN_GENRE]-(m:Movie)
WHERE m.imdbRating IS NOT NULL
AND m.poster IS NOT NULL
RETURN m.poster AS poster
ORDER BY m.imdbRating DESC LIMIT 1
}
RETURN g {
.name,
link: '/genres/'+ g.name,
poster: poster,
movies: count { (g)<-[:IN_GENRE]-() }
} as genre
ORDER BY g.name ASC
""";
var genres = session.executeRead(
tx -> tx.run(query)
.list(row ->
row.get("genre").asMap()));
// Return results
return genres;
}
}Testing
To test that this functionality has been correctly implemented, run the following code in a new terminal session:
mvn test -Dtest=neoflix._09_GenreListTestThe test file is located at src/test/java/neoflix/_09_GenreListTest.java.
Are you stuck? Click here for help
If you get stuck, you can see a working solution by checking out the 09-genre-list branch by running:
git checkout 09-genre-listYou 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
Which genre has the highest movie count?
After the test has succeeded, the test suite will log the name of the genre with the greatest number of movies.
Enter the name of the genre below and click Check Answer.
-
✓ Drama
Hint
You can also find the answer by running the following Cypher statement:
MATCH (g:Genre)
RETURN g.name ORDER BY count{ (g)<-[:IN_GENRE]-() } DESC LIMIT 1Copy the answer without any quotes or whitespace.
Lesson Summary
In this Challenge, you updated the GenreService to retrieve a list of genres from the database.
In the next Challenge, you will update the GenreService to query Neo4j to find the details of an individual genre.