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4: Create the register Author command

For this step you will need to create classes and an interface in two different packages in our project.

Command​

We need to create a REST endpoint that allows us to register Authors.

### Register an author
POST /authors/commands/register HTTP/1.1
Host: localhost:8080
Content-Type: application/json

{
  "firstName": "PLACE_YOUR_FIRST_NAME",
  "lastName": "PLACE_YOUR_LAST_NAME"
}

This endpoint should create an Author from the given Data Transfer Object (DTO) (or payload) and call the register function of an author on the domain layer service (a port / interface). The standard response should be empty with status code 202.

Tip: You can add the above snippet in a file ./http/AuthorCommands.http which allows you to execute the request from inside your IDE (if supported, IntelliJ does).

Domain Core​

According to the domain model we need to create the class /domain/author/Author.java in our domain package. To keep control of the creation of our aggregates we make the all args constructor private and instead create a factory method public static Author createAuthor(String firstName, String lastName). Only our factory method will access the private all args constructor. That way we can keep control of the creation of Authors at all times outside our domain package. For now that is all we need. No getters, no setters or builders needed for now. In case you are asking yourself: And what about the id? Rest assured! We will solve this one later. It remains null for now.

author.png

The data port​

In order to be able to interact with our domain, we need to define a port (interface) called /domain/author/AuthorService.java in our domain package. The required members can be found in the domain model. Afterwards, we inject this into our AuthorCommands.javaclass in the constructor (you could autowire it but let's stick to constructor injection).

Nice to know: this complies with the SOLID principle of 'dependency inversion'. Good for us :)

author-service.png

The Data Layer​

No injection without at least one Spring Bean implementing the interface. After having injected the interace, at least INtelliJ will show a warning or error that it requires at least one implementation.In /data/author/AuthorServiceImpl.java we implement /domain/author/AuthorService.java and annotate it with the @Service annotation from Spring. For now, simply add a log statement of your choice to the implementation of the method void registerAuthor(Author author).

Validation​

Let's test our code. Feel free to write your own test. Alternatively, copy and paste this test class into your project and run it. All should be green :-).

@SpringBootTest
@AutoConfigureMockMvc
class AuthorCommandsTest {

    @Autowired
    private MockMvc mockMvc;

    @Autowired
    private ObjectMapper objectMapper;

    @Test
    void register() throws Exception {
        //given
        var registerAuthorPayloadJson = objectMapper.writeValueAsString(new RegisterAuthorPayload("firstName", "lastName"));

        //when //then
        mockMvc.perform(post("/authors/commands/register")
                        .contentType(MediaType.APPLICATION_JSON)
                        .content(registerAuthorPayloadJson))
                .andExpect(status().isAccepted());
    }
}

OPTIONAL: Run the app on localhost​

By the way, if you run the docker compose file ./docker-compose.yml and start the Spring app you can also test your API at runtime manually. Got to http/AuthorCommands.http and run the request against your localhost:8080.

if (allTestsGreen == true) {
    log.info("DONE! Let's move on to the next topic: **Persisting Data**.")}
else{
    log.error("Shout for help!") || (git stash && git checkout 4-create-author-command-done)
}