How do you deal with legacy or external systems that do not follow factory abstraction principles in DDD?

When integrating legacy or external systems not aligned with DDD's factory abstraction principles, try these: 1. Facade Pattern: Simplify interactions with a facade layer. 2. Adapter Pattern: Translate system interfaces to fit your domain. 3. Anti-Corruption Layer (ACL): Shield your domain from external complexities. 4. Service Wrappers: Encapsulate interactions within dedicated services. 5. Fallback Mechanisms: Gracefully handle unavailability or issues. 6. Incremental Refactoring: Gradually align systems with DDD. 7. Testing and Mocking: Ensure behavior with tests and mocks. 8. Documentation and Communication: Document interactions and limitations clearly. These methods aid integration while managing deviations from DDD principles.

In my experience as a banking expert, using an ACL has been effective in translating between the bank's domain model and legacy systems. The ACL acts as a barrier, preventing the external system's complexities from leaking into our core banking domain. It allows us to interact with the legacy system using the banking domain's ubiquitous language, keeping our domain model clean and focused.

Según mi experiencia, antes de implementar una capa anticorrupción, el cuál es un patrón táctico válido para éstos casos, es importante analizar previamente el Contexto, hacer una Context Mapping nos sería de mucha utilidad dado que tenemos que analizar bien cuál es la interrelación que tenemos con los sistemas existentes, ver que modelos hacen sentido, esto en el caso de tener algo parecido a una shared kernel o librería compartida en donde se tienen varios modelos compartidos que son parte del dominio. Una vez tenemos eso y entendemos nuestro contexto, por supuesto, lo recomendable es implementar una Anticorruption layer el cuál nos permita proteger nuestros modelos y asegurar su significado y sentido dentro de nuestro Bounded context.

We've successfully used the Adapter pattern to integrate with external systems that have incompatible interfaces. By creating an adapter that wraps the external system and provides a banking domain-friendly interface, we can seamlessly interact with it using our domain objects and concepts. The adapter handles the translation and communication with the external system behind the scenes.

When dealing with complex legacy systems in our banking environment, the Facade pattern has been a valuable tool. We create a simplified facade layer that provides a higher-level interface tailored to our banking domain's needs. This facade encapsulates the intricacies of the legacy system, exposing only the relevant functionalities required by our domain. It greatly simplifies the interaction and reduces the coupling between our banking system and the legacy system.

In the banking domain, we often need to integrate with legacy databases or external data sources. The Repository pattern has been instrumental in abstracting away the data access complexities. By defining repository interfaces aligned with our banking domain's language and concepts, we can encapsulate the data access logic and provide a clean, domain-focused API for querying and persisting banking-related data. This allows our domain model to remain independent of the underlying data storage mechanism.