feat: data architecture transformation - event-driven decoupling with shared-events module

[devin-ai-integration]

Summary

Complete data architecture transformation to decouple cross-service data dependencies and introduce event-driven data synchronization across the banking microservices codebase.

Changes

1. New shared-events Maven module (shared-events/)

• Common Axon Framework event definitions: CustomerCreatedEvent, CustomerUpdatedEvent, AccountCreatedEvent, AccountCreditedEvent, AccountDebitedEvent, AccountTransferredEvent, AccountActivatedEvent, AccountSuspendedEvent, AccountDeletedEvent
• Shared enums: AccountStatus, Currency, OperationType
• Base event class with common fields (id, eventDate, eventBy)

2. Removed duplicated customer email from account-service

• Removed email field from Account entity, AccountAggregate, CreateAccountCommand, AccountCreatedEvent
• Accounts now reference customers only by customerId
• Updated AccountEmailCustomerId validation entity to only track customerId
• Updated AccountCommandRestController to no longer pass email during account creation

3. Refactored notification-service to consume Axon events

• Added Axon Framework + OpenFeign + JPA dependencies
• Created AccountEventNotificationHandler that subscribes to all account events via @EventHandler
• Added CustomerRestClient Feign client to look up customer email from customer-service
• Added AccountCustomerMapping entity + repository for account-to-customer ID mapping (populated from AccountCreatedEvent)
• Removed direct REST notification calls from account-service's AccountEventHandlerService
• Deleted NotificationService, NotificationServiceImpl, NotificationRestClient, NotificationRequestDTO from account-service

4. CustomerEventHandler in account-service

• New CustomerEventHandler listens for CustomerUpdatedEvent from shared-events
• Updates account projection timestamps when customer data changes

5. Flyway migration

• V1__remove_email_from_account.sql removes email column and unique constraint from account tables
• Configured Flyway with baseline-on-migrate=true for existing databases

6. Updated DTOs and API contracts

• Account creation API no longer requires/returns email
• All internal event/command constructors updated to exclude email parameter

7. Comprehensive unit tests (34 tests passing)

• Updated AccountAggregateTest (8 tests) - removed email from all event/command constructors
• Updated AccountEventHandlerServiceTest (6 tests) - removed notification service mocks
• New CustomerEventHandlerTest (2 tests) - tests for customer update projection sync
• New AccountEventNotificationHandlerTest (8 tests) - tests for all event notification flows including customer lookup, mapping persistence, and error handling

Review & Testing Checklist for Human

• Verify the Flyway migration V1__remove_email_from_account.sql runs correctly against your database (the DROP COLUMN IF EXISTS syntax is MySQL/MariaDB specific)
• Verify the shared-events module event class FQCNs are compatible with your Axon Server serialization configuration (if migrating from existing event store data)
• Test end-to-end flow: create a customer, create an account, verify notification-service receives the event and sends email notification
• Verify the AccountCustomerMapping in notification-service is correctly populated and used for non-creation events (credit, debit, suspend, etc.)
• Check that axon.axonserver.enabled configuration is set correctly for your deployment environment

Notes

• The account-service's internal event classes (in common.event package) are kept for backward compatibility with the Axon event store serialization. The shared-events module provides cross-service event contracts.
• The local enums in account-service now have conversion methods (toShared()/fromShared()) for interoperability with shared-events enums.
• The notification-service uses an H2 in-memory database for the AccountCustomerMapping projection - consider switching to a persistent store for production use.
• Customer-service POM now includes Axon Framework dependency to support publishing CustomerCreatedEvent/CustomerUpdatedEvent in future iterations.

Link to Devin session: https://app.devin.ai/sessions/c77d3461f3134ff08fec52d68f820311
Requested by: @achalc

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