Add a function

This guide adds a GetMovie function that returns one movie with all of its reviews. The Application layer already has a GetMovieByIdQuery, so all the work happens in Presentation. That’s the point of the layers: new ways in, same rules underneath.

Add a request model in src/Presentation/LambdaFunction/Models/GetMovieRequest.cs. This is the JSON your callers send.

namespace Acme.Reviews.Presentation.LambdaFunction.Models;

/// <summary>
/// Gets one movie and its reviews.
/// </summary>
public record GetMovieRequest
{
    /// <summary>The id of the movie to get.</summary>
    public Guid Id { get; init; }
}

Add a response model in src/Presentation/LambdaFunction/Models/MovieDetail.cs. It reuses the existing Review model.

namespace Acme.Reviews.Presentation.LambdaFunction.Models;

public record MovieDetail(Guid Id, string Title, List<Review> Reviews);

Teach the mapper about it in Mapping/LambdaFunctionMapper.cs. Mapperly writes the code at build time, including the list of reviews.

using AppMovieDetail = Application.Movies.Entities.Movie;
// ...
using PresentationMovieDetail = Models.MovieDetail;

public partial PresentationMovie ToPresentation(AppMovie movie);

public partial PresentationMovieDetail ToPresentation(AppMovieDetail movie);

Register both types with the source-generated serializer in Serialization/LambdaFunctionJsonSerializerContext.cs. Skip this and Lambda can’t read the request.

[JsonSerializable(typeof(Page<Movie>))]
[JsonSerializable(typeof(Page<Author>))]
[JsonSerializable(typeof(Page<Review>))]
[JsonSerializable(typeof(GetMovieRequest))]
[JsonSerializable(typeof(MovieDetail))]
public partial class LambdaFunctionJsonSerializerContext : JsonSerializerContext

Add the function to LambdaFunction.cs. Send opens a scope, runs the query through validation and stops it if the invocation runs out of time.

/// <summary>
/// Gets one movie and every review of it.
/// </summary>
/// <param name="request">The id of the movie.</param>
/// <param name="context">The Lambda invocation context.</param>
/// <returns>The movie and its reviews.</returns>
public async Task<MovieDetail> GetMovie(GetMovieRequest request, ILambdaContext context)
{
    var movie = await this.Send(new GetMovieByIdQuery { Id = request.Id }, context);

    return this.mapper.ToPresentation(movie);
}

Add using Application.Movies.Queries.GetMovieById; at the top.

Test it in tests/Presentation.Tests.Integration/HandlerTests.cs. The class already has a handler with its own seeded database.

[Fact]
public async Task GetMovie_ShouldReturn_TheMovieAndItsReviews()
{
    // Arrange
    var movie = (await this.handler.GetMovies(new ListRequest(), this.context)).Items[0];

    // Act
    var result = await this.handler.GetMovie(new GetMovieRequest { Id = movie.Id }, this.context);

    // Assert
    result.Title.ShouldBe(movie.Title);
    result.Reviews.Count.ShouldBe(movie.ReviewCount);
}

Run it.

docker build . --target run --tag acme-reviews:local
docker run --rm -p 9000:8080 -e Database__SeedSampleData=true acme-reviews:local \
  "Presentation::Acme.Reviews.Presentation.LambdaFunction.Handler::GetMovie"

curl -X POST "http://localhost:9000/2015-03-31/functions/function/invocations" \
  -d '{"id":"e159975e-4e6a-1ffd-713e-1eb9d8d4a593"}'

An unknown id fails with a NotFoundException, and an empty one fails validation, both before your code has to worry about it.