Patrick Lehmann – Senior SAP S/4HANA Developer & Software Architect. Legacy meets Clean Code,
S/4HANA.

The shift to S/4HANA mandates modification-free extensions ("Clean Core"), API-based approaches, and accelerated development cycles through AI assistance for upcoming migrations.

Establishment of a hybrid reference architecture to build know-how for future client migrations, validating full-stack efficiency and side-by-side extensibility on the SAP BTP.

Hands-on full-stack development of an end-to-end application on the SAP BTP. Direct implementation of the backend via Restful Application Programming Model (RAP) and programming of specific logic in the Cloud Application Programming Model (CAP with Node.js). Integration of AI-supported code generation through SAP Joule to accelerate development cycles.

Code proof of maximum full-stack efficiency using SAP BTP services and know-how building for developing a blueprint for SAP BTP utilization.

Technical lead for the S/4HANA introduction at a large public authority. With a focus on compliance with extension standards and mapping complex budgetary requirements (PSM), including successful migration of portions of master and transactional data.

Hands-on implementation of a modification-free backend architecture ("Clean Core") and technical execution of the data migration.

Active development of a decoupled integration layer via SAP AIF and ABAP OO. Built complex CDS views for data modeling. Direct technical implementation of migration logic for over 100,000 critical datasets via Migration Cockpit. Close collaboration with the development team through pair programming and code reviews for quality assurance.

Planned and low-disruption go-live of master data – over 100,000 critical records successfully migrated. Measurable reduction of technical debt through clean, maintainable code and established ABAP unit tests within the team.

A hybrid corporate landscape of classic ERP and new S/4HANA systems had to be coupled with new interfaces and historically grown legacy code. Furthermore, a product for solving legislative requirements was developed.

Code-level modernization of business logic and hands-on development of future-proof, decoupled APIs.

Programming a harmonized interface layer through the intensive use of the RESTful ABAP Programming Model (RAP). Active refactoring of legacy code for clean separation of standard and individual development. Implementation of Test-Driven Development (TDD) by writing automated tests.

Measurable increase in system stability. Enhanced flexibility and upgrade reliability by consistently outsourcing custom logic into clean RAP services.

In the security sector, manual deployment processes and siloed infrastructures led to critical delays and error-prone releases.

Hands-on infrastructure automation and programming of continuous CI/CD pipelines.

Setup and configuration of structured CI/CD pipelines (Jenkins/GitLab). Development of services in Python and Go with TDD (Test-Driven Development). Pragmatic containerization of specific workloads with Docker and their deployment on Cloud Foundry. Direct implementation and enforcement of automated test suites in the deployment process.

Drastic reduction in manual deployment efforts and accelerated time-to-market through fully automated, stable release pipelines with a drastically reduced error rate.

Integration of new functionalities into an existing SAP CRM environment. Long-running processes and inefficient architectural patterns in this business-critical landscape jeopardized operational business and blocked upgrades.

Code-level reengineering, technical upgrade, and deep-dive performance tuning to restore scalability.

In-depth system and performance analysis (Traces, Code Inspector). Hands-on refactoring of complex ABAP OO legacy code and reprogramming of central data models in the WebUI (BOL/GenIL). Script-based and orchestrated migration of sensitive legacy data into optimized table structures.

Noticeable acceleration of business processes at the push of a button, successful system upgrade, and sustainable relief for the database and infrastructure.