step-3-inter-module-communication.md

Inter domain communication

Kata goal

Two domains that need to communicate together.

We represent each domain in an hexagon in order to isolate them.

Implement the communication between two domains that are in the same deployment unit (modular monolith).

Business

We want to verify the format of the business partner code.

There can be multiple reasons to have multiple hexagons:

• In the near future, we will have to implement more controls regarding business partners
• Dedicated team will be in charge of the 2nd hexagon
• 2nd hexagon will be replaced by an external system
• 2nd hexagon will be deployed as dedicated unit (a micro-service usable by other projects)

For now the format we want to check is:

• total length is 20 characters
• example: 'FIHEL-partner 496871'

At the end of the kata you will be able to check your code by using this URL in a browser:

• http://localhost:8080/booking/create/{businessPartnerCode} It should create with a booking with a quantity of 1 and return the sum of all the quantities

Steps

Prepare

• Create businesspartner package (new package for booking management)

Application and port preparation

Present the feature to perform (Driver side)

• Create the businesspartner.port.in package
• Create the ForCheckingBusinessPartnerCode interface
• Add the method boolean isValid(String code)

Prepare the feature to code

• Create the BusinessPartnerVerifier class in the businesspartner package
• Annotate this class with the @Service annotation
• Add the implements ForCheckingBusinessPartnerCode to BusinessPartnerVerifier
• Implement the method with a fake body

Test and implement the rule

• Create the BusinessPartnerVerifierTest
• Create test methods (case true/false)
• Implement the rule in the BusinessPartnerVerifier

class BusinessPartnerVerifierTest {

    private BusinessPartnerVerifier businessPartnerVerifier = new BusinessPartnerVerifier();

    @Test
    void isValid_returnsTrue_whenCodeIs20CharactersLong() {
        boolean result = businessPartnerVerifier.isValid("12345678901234567890");

        assertThat(result).isTrue();
    }

    @Test
    void isValid_returnsFalse_whenCodeIs5CharactersLong() {
        boolean result = businessPartnerVerifier.isValid("12345");

        assertThat(result).isFalse();
    }

}

Prepare the call

• Create the ForVerifyingBusinessPartner interface in the booking.port.out package
• Add the method boolean validate(String code)
• Inject the ForVerifyingBusinessPartner in the BookingManager
• Add the call of the method validate() in the BookingManager and do not create booking if false
• In BookingManagerTest fix the compilation problem by creating a fake ForVerifyingBusinessPartner implementation that always returns true
• In BookingRestController inject the ForVerifyingBusinessPartner using constructor injection

Implement communication between systems

Prepare the adapters

Create the booking out adapter:

• Create the InMemoryBusinessPartnerVerifier class
• Add the implements ForVerifyingBusinessPartner to InMemoryBusinessPartnerVerifier
• Override the method (with an empty body)
• Add the @Repository annotation to the class

Create the business partner in adapter:

• Create businesspartner.adapter.in package
• Create the ProvideBusinessPartnerVerifier class
• Inject ForCheckingBusinessPartnerCode to ProvideBusinessPartnerVerifier
• Create a public boolean validate(String code) method
• Call the validate method from ForCheckingBusinessPartnerCode
• Add the @Component annotation to the class

Implement adapters

Possible implementations:

• Point to point: out knows in
  • Direct in memory
• Publish / subscribe: out publishes, in subscribes
  • Inversion of Dependency

Tips

Direct in memory

In adapter out, inject the adapter in.

Inversion of Dependency

In adapter out create a new interface and implement it the adapter in

Inject the new interface in the InMemoryBusinessPartnerVerifier using Spring