demo.md

Demo

Step 1 - Domain

It is a simple module which is composed of:

• domain: Domain POJOs
• api: Application Provider Interface - Interfaces which expose services to interact with the domain (customer sign-up, adding product to customer's cart, create product...)
• spi: Service Provider Interface - Interfaces which expose services that are required by the domain to manage data (eg. persistence)

NOTHING should enter domain! It has no dependency to implementation frameworks (spring / jpa / ...).

Examples of modules to interact with the domain:

Step 2 - Memory-persistence module

Module to implement the interfaces exposed by the domain (as SPI) so we store the products and customers in memory. To do so, we need to implement both repositories as below:

public class InMemoryProductRepository implements ProductRepository {

  private List<Product> inMemoryProducts = API.List();

  public Product addProduct(Product product) {
    this.inMemoryProducts = getInMemoryProducts().append(product);
    return product;
  }

  public void deleteProduct(UUID productId) {
    this.inMemoryProducts = getInMemoryProducts().filter(product -> !product.getId().equals(productId));
  }

  public Option<Product> findProductByCode(String code) {
    return getInMemoryProducts().find(product -> product.getCode().equals(code));
  }

  public List<Product> findAllProducts() {
    return getInMemoryProducts();
  }
}

Step 3 - First application to use services

Console application which uses dependencies to domain and this in-memory persistence module:

• Quickly test business logic in an application
• Fast feedback

Step 4 - Changing business logic

Ok we can now create product and customers but we can create product without price :-(

Let's add a new rule: Prevent product to be created without price | with price <= 0

Step 5 - Rest client

Module to implement a spring boot rest client module to expose some endpoints using the domain services.

It only contains:

• CustomerController.java: controller to handle actions to do about customers (create / add product to cart / find)
• ProductControler.java: controller to handle actions to do about products (create / update / find)

---

Note:

• It is not necessary to implement all services exposed by the domain.
• We can also transform the exposed items using DTO

---

Step 6 - Postgres

Module to implement the persistence system using Postgres as for memory-persistence:

@Repository
@AllArgsConstructor
public class PostgresProductRepository implements ProductRepository {

  private PostgresSpringDataProductRepository postgresSpringDataProductRepository;

  @Override
  public Product addProduct(Product product) {
    return postgresSpringDataProductRepository.save(PostgresProduct.fromProduct(product))
        .toProduct();
  }

  @Override
  public void deleteProduct(UUID productId) {
    postgresSpringDataProductRepository.deleteById(productId);
  }

  @Override
  public Option<Product> findProductByCode(String code) {
    return ofOptional(postgresSpringDataProductRepository.findByCode(code).map(PostgresProduct::toProduct));
  }

  @Override
  public List<Product> findAllProducts() {
    return ofAll(postgresSpringDataProductRepository.findAll())
        .map(PostgresProduct::toProduct);
  }
}

Here we need to handle DAO so objects stored in Postgres are defined as below:

@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
@Wither
public class PostgresProduct {

  @Id
  private UUID id = randomUUID();
  private String code = "";
  private String label = "";
  private BigDecimal price = ZERO;  
}

Step 7 - Web application

Spring boot application which uses dependencies to the domain but also postgres-persistence, memory-persistence and rest-client so we can interact with the domain using curl commands and store data in-memory.

• Create a product: curl --header "Content-Type: application/json" --request POST --data '{ "code": "1616", "label": "Easybreath", "price": 25.95 }' http://localhost:8080/products
• List products: curl --header "Content-Type: application/json" --request GET http://localhost:8080/products
• Find product: curl --header "Content-Type: application/json" --request GET http://localhost:8080/products/1616
• Create a customer: curl --header "Content-Type: application/json" --request POST --data 'rdelgatte' http://localhost:8080/customers
• Find customer by login: curl --header "Content-Type: application/json" --request GET http://localhost:8080/customers/rdelgatte
• Add product to customer's cart: curl --header "Content-Type: application/json" --request PATCH --data '1616' http://localhost:8080/customers/rdelgatte

Configuration / Dependencies

We need to explicitly define the ProductService and CustomerService so we provide the persistence module to use for each.