Rating Movies

The Request Lifecycle

Before we start, let’s take a look at the request lifecycle when saving a review. If you prefer, you can skip to Saving a Rating.

On every Movie page, the user is invited to rate a movie on scale of 1 to 5. The form pictured to the right gives the user the ability to select a rating between 1 and 5 and click submit to save the rating.

When the form is submitted, the website sends a request to /api/account/ratings/{movieId} and the following will happen:

A rating is represented in the graph a relationship going from a :User to a :Movie node with the type :RATED. The relationship has two properties; the rating (an integer) and a timestamp to represent when the relationship was created.

After the data is saved, the UI expects the movie details to be returned, with an additional property called rating, which will be the rating that the user has given for the movie.

Let’s take a look at the existing method in the RatingService.

async add(userId, movieId, rating) {
  // TODO: Convert the native integer into a Neo4j Integer
  // TODO: Save the rating in the database
  // TODO: Return movie details and a rating

  return goodfellas
}

Your challenge is to replace the TODO comments in this method with working code.

Saving a Rating

If you take the the comments one-by-one, you will need to convert the native integer into a Neo4j Integer, save the rating in the database and then return movie details and a rating.

import { int } from 'neo4j-driver'

// ...

// Convert the native integer into a Neo4j Integer
rating = int(rating)

toInteger(20.0) // 20

// Save the rating to the database

// Open a new session
const session = this.driver.session()

// Save the rating in the database
const res = await session.executeWrite(
  tx => tx.run(
    `
      MATCH (u:User {userId: $userId})
      MATCH (m:Movie {tmdbId: $movieId})
      MERGE (u)-[r:RATED]->(m)
      SET r.rating = $rating,
          r.timestamp = timestamp()
      RETURN m {
        .*,
        rating: r.rating
      } AS movie
    `,
    { userId, movieId, rating, }
  )
)

await session.close()

// Check User and Movie exist
if ( res.records.length === 0 ) {
  throw new NotFoundError(
    `Could not create rating for Movie ${movieId} by User ${userId}`
  )
}

// Return movie details and rating
const [ first ] = res.records
const movie = first.get('movie')

return toNativeTypes(movie)

Working Solution

async add(userId, movieId, rating) {
  // Convert the native integer into a Neo4j Integer
  rating = int(rating)

  // Save the rating to the database

  // Open a new session
  const session = this.driver.session()

  // Save the rating in the database
  const res = await session.executeWrite(
    tx => tx.run(
      `
        MATCH (u:User {userId: $userId})
        MATCH (m:Movie {tmdbId: $movieId})
        MERGE (u)-[r:RATED]->(m)
        SET r.rating = $rating,
            r.timestamp = timestamp()
        RETURN m {
          .*,
          rating: r.rating
        } AS movie
      `,
      { userId, movieId, rating, }
    )
  )

  await session.close()

  // Check User and Movie exist
  if ( res.records.length === 0 ) {
    throw new NotFoundError(
      `Could not create rating for Movie ${movieId} by User ${userId}`
    )
  }

  // Return movie details and rating
  const [ first ] = res.records
  const movie = first.get('movie')

  return toNativeTypes(movie)
}

Testing

To test that this functionality has been correctly implemented, run the following code in a new terminal session:

npm run test 06

The test file is located at test/challenges/06-rating-movies.spec.js.

git checkout 06-rating-movies