We will now add an endpoint to fetch a movie.
You are provided a PostgresqlRepository that contains all the SQL needed to work with Postgres. We have done this for you so that you do not have to write any of the SQL on your own.
We are using a library called doobie. If we look at this file, we have one function for each of our endpoints already implemented. Keep in mind that the return type of each function is an IO.
The function that is useful for us for this endpoint is fetchMovie, which has type signature of MovieId => IO[Option[Movie]].
The Service typically has business logic. For example, it may call multiple repositories and then validate their responses to construct another response.
Pay attention to the types we are using in the Service. We have a MovieId (not a Long!) and we are returning a Movie. Not only do these types improve readability, they provide additional safety. We can't accidentally supply a CustomerId where a MovieId is expected.
There's nothing to do with HTTP or Json responses here.
Complete exercise
Run unit test: FetchMovieServiceSpec
The fetch method has a movieId passed in as a Long. This is the id that is in the path of the request GET movie/123. The return type is IO[Response[IO]]. This is Http4s' response type.
The Controller layer takes care of HTTP request and response so the Service layer does not need to.
To complete this exercise, you need to complete the following first:
- Encoder for
Review - Encoder for
Movie
Complete exercise
Run unit test: FetchMovieControllerSpec
Notice that AppRoutes has two unused handlers: fetchMovieHandler and fetchEnrichedMovieHandler. Ignore the latter for now.
There is an unimplemented route for fetching a single movie, where the id of the movie is extracted out using LongVar.
(LongVar is an extractor. If a Long matches in that spot, we get access to it on the right hand side.)
Implement this route by calling fetchMovieHandler.
Run unit test: AppRoutesSpec
Now let's wire the Service and Controller up in AppRuntime.
Pass in the handler from the newly instantiated fetchMovieController into appRoutes.
Start the app using ./auto/start-local and curl http://localhost:9200/movies/1 to get Titanic back!