Sr. C# / .NET Developer

SmartIMS Inc.; Village of Hamilton (NY); On-site; USD 120,000 - 190,000; Full time

Job summary

SmartIMS Inc. is seeking a Sr. .NET Developer to modernize a COBOL-derived codebase into a maintainable .NET solution. You will design & implement ASP.NET Core Web APIs that power the Angular front end, and refactor legacy batch logic with exact decimal/financial calculations.

You will lead EF Core data access against PostgreSQL, optimize performance, and ensure high-quality delivery with unit tests and CI/CD integration. Mentoring and architectural guidance are key parts of the role.

Qualifications

• 15 years of professional C#/.NET software engineering with senior/lead responsibilities.
• Deep expertise in C#/.NET including async programming and modern language features.
• Expert-level EF Core: modeling, migrations, queries, concurrency.

Responsibilities

• Refactor COBOL-derived C# into idiomatic, maintainable .NET.
• Design and implement ASP.NET Core Web API back-end for Angular UI.
• Refactor legacy batch logic to ensure correctness and performance.
• Collaborate on CI/CD, quality gates, and security standards.
• Mentor mid/junior developers and perform code reviews.

Skills

Senior-level C#/.NET

Async programming

Unit/integration testing

Code reviews/mentoring

Design patterns/SOLID

Read/refactor large codebases

Performance optimization

CI/CD practices

AWS usage

PostgreSQL database design

Entity Framework Core

Tools

EF Core

ASP.NET Core Web API

PostgreSQL

AWS (ECS/EKS, RDS, S3)

Npgsql

Job description

Title: Sr. .Net Developer

Location: Hamilton, NJ

Duration: 12+ Months

Description:

C# / .NET Engineering

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)

Entity Framework / Data Layer

• 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

Technical Leadership

• 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

Quality, Testing & Delivery

• 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

Required Qualifications

• 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

• 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

• Establish the C#/.NET and EF Core standards, patterns, and reference implementation the team will follow
• Refactor a representative set of converted programs (including a benefit-calculation and a batch program) to clean, tested, performant C# validated against the legacy baseline
• Define the EF Core data-access approach against PostgreSQL, including query-performance guardrails for batch workloads
• Mentor the team and set the code-review/quality bar