C#/.NET Engineer

PSR Associates•Hamilton Township, NJ

3d•Hybrid

About The Position

PSR Associates is a consulting and talent solutions firm that connects qualified IT professionals with great opportunities. Whether you're looking for a contract or permanent position, we can help you find the right fit for your skills and experience. We have a team of experienced recruiters who know the IT industry inside and out, and we work with you every step of the way to ensure a smooth and successful transition. PSR Connecting Talent, Crafting Success. C#/.NET Engineer Position Description We are seeking a C#/.NET Engineer to join our team. The selected candidate will work onsite for the first 30 days and then will transition to a hybrid role consisting of three (3) days each week onsite in Hamilton Township, NJ and two (2) days each week remotely. Summary: Our customer is modernizing a large, mission-critical Client Bull mainframe benefits system (FAMIS) — converting ~1.5M lines of COBOL and ~160K lines of JCL to C#/.NET, migrating an IDS-II hierarchical database to PostgreSQL, and deploying on AWS. Converted code is delivered by an automated modernization vendor in an "as-is" state. This Lead/Principal role owns the refactoring of that converted code into clean, maintainable, high-performance, production-grade C#/.NET, defines the data-access architecture using Entity Framework Core against PostgreSQL, sets engineering standards for the team, and safeguards functional equivalence to the legacy system. This is a benefits system serving NJ families — correctness, performance within the nightly batch window, and maintainability are paramount.

Requirements

12-15 years of professional C#/.NET software engineering, including senior/lead responsibilities
Deep expertise in C# and the .NET platform (.NET Framework and .NET Core / .NET 6/8+), including async programming, memory/performance optimization, and modern language features
Expert-level Entity Framework / EF Core: entity modeling, Fluent API, migrations, query optimization, transactions, concurrency, provider-specific behavior
Strong relational database skills; PostgreSQL strongly preferred (Oracle/SQL Server acceptable) — schema design, indexing, query tuning, stored procedures
ASP.NET Core Web API design (REST) for front-end integration
Solid software design: SOLID, design patterns, domain modeling, layered/clean architecture, dependency injection
Testing discipline: unit/integration/regression testing frameworks; TDD/mocking
Git, CI/CD, and static code analysis (SonarQube)
Proven ability to read, reason about, and safely refactor large, unfamiliar codebases
Exceptional attention to correctness — financial/benefit calculation accuracy

Nice To Haves

Legacy modernization experience — COBOL-to-C#/Java conversion, mainframe migration, or automated-transformation tooling
Understanding of mainframe concepts (COBOL, JCL, batch processing, hierarchical/CODASYL databases like IDS-II/IMS) — to reason about source behavior
High-volume batch processing performance tuning
AWS experience (ECS/EKS, Lambda, RDS for PostgreSQL, S3, CloudWatch, IaC/CloudFormation)
Experience integrating with enterprise job schedulers (Stonebranch, Control-M, CA7)
Government / benefits / healthcare or other regulated, high-correctness domains
Npgsql specifics, EF Core performance internals, or ORM migration experience

Responsibilities

Refactor machine-converted, COBOL-derived C# into idiomatic, maintainable .NET — meaningful naming, proper OO/domain design, separation of concerns, dependency injection
Work in .NET (Core) / .NET (latest version); apply modern C# language features (LINQ, async/await, records, pattern matching, nullable reference types, generics)
Design and implement service layers, domain models, and APIs (ASP.NET Core Web API) that back the Angular UI
Refactor legacy batch/procedural logic (converted from COBOL/JCL) into maintainable, testable .NET; handle exact decimal/financial arithmetic (decimal, rounding rules) to preserve benefit-calculation correctness
Optimize performance to meet the nightly batch window (profiling, memory management, async I/O, parallelism where safe)
Own the data-access architecture using Entity Framework Core against PostgreSQL (Npgsql provider)
Refactor the auto-generated/converted data-access layer into a clean, performant EF Core model
Design entity models, DbContext configuration, Fluent API mappings, relationships, keys, and indexes reflecting the IDS-II → PostgreSQL schema (168 tables, 4,024+ fields)
Optimize EF Core queries (eager/lazy/explicit loading, projection, AsNoTracking, compiled queries, batching) to avoid N+1 and meet performance SLAs on high-volume batch operations
Manage EF Core migrations, concurrency handling, transactions, and connection resiliency
Map legacy data types and semantics correctly (packed decimals, fixed-width, EBCDIC-origin data, condition codes) to PostgreSQL/EF types without behavioral drift
Contribute to the COBOL-field → PostgreSQL-column → business-term data dictionary
Define and enforce C#/.NET coding standards, architecture patterns, and refactoring guidelines for the engineering team
Serve as senior technical authority on the converted codebase; make cross-cutting design decisions
Mentor mid/junior C# developers; perform code reviews; drive engineering quality
Partner with the Technical Manager/Architect on target architecture and the refactoring strategy
Ensure functional equivalence: build unit and regression tests (xUnit/NUnit, Moq) to validate refactored code against the legacy baseline; fix FET-surfaced defects
Integrate with CI/CD (AWS CodeBuild/CodePipeline), enforce quality/security gates (SonarQube, static analysis, secure coding/OWASP)
Collaborate with FAMIS SMEs to preserve business logic (eligibility, benefit calculation, payments, EBT)
Deliver incrementally within Scrum; document design and decisions