Now for another challenge.
In this challenge, you will use the knowledge gained so far in this course to add new functionality to the API.
You will modify the all() method of the MovieService to do the following:
Once you have completed the challenge, you will be asked to run a unit test to verify that the code has been correctly implemented. If the test runs correctly, the title of the highest rated movie will be logged.
You will need this value to verify that the test has run correctly.
Exploring the Code
Before you start, let’s take a look at the code.
If you are not interested in the code, you can skip straight to Implementing Read Transactions.
If you start the application with mvn compile exec:java and access the app at http://localhost:3000, you will see two lists on the home page; one for Popular Movies and one for Latest Releases.
Both of these lists are populated by a request to http://localhost:3000/api/movies with some additional request query parameters, feel free to open that URL in your browser, you should see the JSON response.
Route Handler
You can find the route handler, the function that handles the request, in src/main/java/neoflix/routes/MovieRoutes.java:
Unresolved directive in lesson.adoc - include::https://raw.githubusercontent.com/neo4j-graphacademy/llm-vectors-unstructured/main/src/main/java/neoflix/routes/MovieRoutes.java[tag=list]Within the route handler, you can see that:
-
A new instance of the
MovieServiceis created with the Driver instance that you created in Adding the Driver passed to the constructor. -
The
sort,order,limitandskipvalues are extracted from the request. This allows us to apply sorting and pagination to the results. -
The
userIdis also extracted from the request. -
The query results are retrieved via the
all()method and are returned by the handler as JSON.
The Movie Service
The magic happens in the MovieService, located at src/main/java/neoflix/services/MovieService.java.
For this route, we are concerned with the all() method.
If we take a closer look at the all() method, we can see that it currently returns a hardcoded list of popular movies from the popular.json fixture.
Unresolved directive in lesson.adoc - include::https://raw.githubusercontent.com/neo4j-graphacademy/llm-vectors-unstructured/main/src/main/java/neoflix/services/MovieService.java[tag=all]You will need to replace these TODO comments with working code to complete the challenge.
Implementing Read Transactions
As you learned in the Sessions and Transactions lesson, you will complete code to open a new session and run the query within a Read Transaction.
Then, finally you add code to extract and return the results.
Open a new Session
Within the all() method, first open a new session:
Unresolved directive in lesson.adoc - include::https://raw.githubusercontent.com/neo4j-graphacademy/llm-vectors-unstructured/main/src/main/java/example/Index.java[tag=session]Execute a Cypher statement within a new Read Transaction
The Cypher statement itself is similar to this one, only that the property that’s ordered by will be dynamically inserted based on user interaction from the API query parameters.
// ordering will be dynamic in implementation
MATCH (m:Movie)
WHERE m.title IS NOT NULL
RETURN m {
.*
} AS movie
ORDER BY m.title ASC
SKIP $skip
LIMIT $limitThis session then provides an executeRead() method for which you pass a callback/lambda to represent the unit of work.
The function will have one argument passed to it, a Transaction instance that you can use to execute a Cypher statement using the run() method.
The run() method accepts two arguments:
-
The Cypher statement as a string, using query parameters (placeholders prefixed with
$). -
An object containing the names and values of the parameters.
Unresolved directive in lesson.adoc - include::https://raw.githubusercontent.com/neo4j-graphacademy/llm-vectors-unstructured/02-movie-lists/src/main/java/neoflix/services/MovieService.java[tag=allcypher]%s instead, which we would love to avoid.Extract a list of Movies from the Result
Now that you have a complete result assigned to the res variable, you
-
use the
list()function to convert each row, -
grab each
movienode from the rowRecord -
turn the node properties into a Java Map with the
asMap()method.
Unresolved directive in lesson.adoc - include::https://raw.githubusercontent.com/neo4j-graphacademy/llm-vectors-unstructured/02-movie-lists/src/main/java/neoflix/services/MovieService.java[tag=allmovies]Return the Results
Finally, update the return statement to return the movies list extracted above.
Unresolved directive in lesson.adoc - include::https://raw.githubusercontent.com/neo4j-graphacademy/llm-vectors-unstructured/02-movie-lists/src/main/java/neoflix/services/MovieService.java[tag=return]Working Solution
Click here to reveal the completed all() method
Unresolved directive in lesson.adoc - include::https://raw.githubusercontent.com/neo4j-graphacademy/llm-vectors-unstructured/02-movie-lists/src/main/java/neoflix/services/MovieService.java[tag=all]Testing
To test that this functionality has been correctly implemented, run the following code in a new terminal session:
mvn test -Dtest=neoflix._02_MovieListTestThe test file is located at src/test/java/neoflix/_02_MovieListTest.java.
Are you stuck? Click here for help
If you get stuck, you can see a working solution by checking out the 02-movie-lists branch by running:
git checkout 02-movie-listsYou 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
Highest Rated Movie
The final test in the suite logs out the name of the highest rated movie according to the imdbRating property on each movie.
Enter the title of the highest rated movie.
-
✓ Band of Brothers
Hint
You can also find the answer by running the following Cypher statement:
MATCH (m:Movie)
WHERE m.imdbRating IS NOT NULL
RETURN m.title
ORDER BY m.imdbRating DESC LIMIT 1Copy the answer without any quotes or whitespace.
Solution
The answer is Band of Brothers.
Lesson Summary
In this Challenge, you used your knowledge of sessions and transactions to retrieve a list of Movie nodes from the database.
If you now open the API endpoint or the application UI for popular movies you should see the list coming from your database. Congratulations 🎉.
In the next Challenge about user management, you will learn to write data to the database.