In the previous Challenge, we hardcoded a favorite property on the return to the calls in the FavoriteService.
We did this because we could guarantee the value based on the query being executed.
This won’t be possible in the MovieService.
Your next challenge is to modify the MovieService to dynamically determine whether a movie is on the current user’s My Favorite List.
This challenge has one part:
Running Multiple Queries within a Transaction
So far, you have only used the tx Transaction within the Unit of Work to run a single query.
This will be fine for the majority of cases, but there may also be scenarios where more than one Query may be required.
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.
Creating a Reusable Method
At the bottom of the MovieService, a placeholder getUserFavorites() method exists which is currently hardcoded to return an empty array.
private List<String> getUserFavorites(TransactionContext tx, String userId) {
return List.of();
}The purpose of this method is to run a Cypher statement against the Transaction object passed as the first parameter, which will find all of the user’s favorite movies and return a list of tmdbId properties.
Your challenge is to modify this method to retrieve that list of Movie ID’s and then call this function from the Read Transaction in the all() method.
Finding Favorites
Modify the getUserFavorites() method to run the following query against the tx parameter.
Click here to reveal the Cypher statement
This query should only run if a user is logged in for the current request, and therefore the userId parameter is not null.
MATCH (u:User {userId: $userId})-[:HAS_FAVORITE]->(m)
RETURN m.tmdbId AS idWorking Solution
Click here to reveal the completed getUserFavorites() method
private List<String> getUserFavorites(TransactionContext tx, String userId) {
// If userId is not defined, return an empty list
if (userId == null) return List.of();
var favoriteResult = tx.run("""
MATCH (u:User {userId: $userId})-[:HAS_FAVORITE]->(m)
RETURN m.tmdbId AS id
""", Values.parameters("userId",userId));
// Extract the `id` value returned by the cypher query
return favoriteResult.list(row -> row.get("id").asString());
}Adding the getUserFavorites call
Inside the all() method, we have used to just execute a single tx.run().
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.run 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 all() 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.
// Execute a query in a new Read Transaction
var movies = session.executeRead(tx -> {
// Get an array of IDs for the User's favorite movies
var favorites = getUserFavorites(tx, userId);
// Retrieve a list of movies with the
// favorite flag appened to the movie's properties
Params.Sort sort = params.sort(Params.Sort.title);
String query = String.format("""
MATCH (m:Movie)
WHERE m.`%s` IS NOT NULL
RETURN m {
.*,
favorite: m.tmdbId IN $favorites
} AS movie
ORDER BY m.`%s` %s
SKIP $skip
LIMIT $limit
""", sort, sort, params.order());
var res= tx.run(query, Values.parameters( "skip", params.skip(), "limit", params.limit(), "favorites",favorites));
// Get a list of Movies from the Result
return res.list(row -> row.get("movie").asMap());
});// Execute a query in a new Read Transaction
var movies = session.executeRead(tx -> {
// Retrieve a list of movies with the
// favorite flag appened to the movie's properties
Params.Sort sort = params.sort(Params.Sort.title);
String query = String.format("""
MATCH (m:Movie)
WHERE m.`%s` IS NOT NULL
RETURN m {
.*
} AS movie
ORDER BY m.`%s` %s
SKIP $skip
LIMIT $limit
""", sort, sort, params.order());
var res= tx.run(query, Values.parameters( "skip", params.skip(), "limit", params.limit()));
// Get a list of Movies from the Result
return res.list(row -> row.get("movie").asMap());
});Testing
To test that this functionality has been correctly implemented, run the following code in a new terminal session:
mvn test -Dtest=neoflix._08_FavoriteFlagTestThe test file is located at src/test/java/neoflix/_08_FavoriteFlagTest.java.
Are you stuck? Click here for help
If you get stuck, you can see a working solution by checking out the 08-favorite-flag branch by running:
git checkout 08-favorite-flagYou 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
If the test has run successfully, a user with the email address graphacademy.flag@neo4j.com will have added Band of Brothers, the most popular movie in the dataset to their list of favorites.
Hint
You can run the following query to check for the user within the database.
If the shouldVerify value returns true, the verification should be successful.
MATCH (u:User {email: "graphacademy.flag@neo4j.com"})-[:HAS_FAVORITE]->(:Movie {title: 'Free Willy'})
RETURN true AS shouldVerifySolution
The following statement will mimic the behaviour of the test by first finding the movie with the highest .imdbId rating and merging a new :User node into the graph with the email address graphacademy.flag@neo4j.com.
The test then merges a :HAS_FAVORITE relationship between the user and movie.
MATCH (m:Movie) WITH m
WHERE m.imdbRating IS NOT NULL
WITH m
ORDER BY m.imdbRating DESC LIMIT 1
MERGE (u:User {userId: '9f965bf6-7e32-4afb-893f-756f502b2c2a'})
SET u.email = 'graphacademy.favorite@neo4j.com'
MERGE (u)-[r:HAS_FAVORITE]->(m)
RETURN *Once you have run this statement, click Try again…* to complete the challenge.
Module Summary
In this module, you have updated the project to read data from, and write data to Neo4j. You have also learned about some of the considerations that we need to make when working with the Cypher type system in our Java application.
In the Project Backlog module, you will continue to implement the remaining missing pieces of functionality. This isn’t strictly required, but will be good practice for your development journey ahead.