C# Backend Development: Minimal APIs & PostgreSQL

A self-study course on backend development in C#. You’ll build a complete REST API running entirely on your own computer — no cloud accounts needed — but the technology and structure is the same as when developing for cloud deployment.

This material was originally written for 4th-semester engineering students at Aarhus University working on a telemedicine project that needed a backend server and database. It’s equally useful as a standalone introduction to backend development. It’s also on GitHub — comments and improvement suggestions are welcome.

What you’ll build

CLIENT (Browser/Postman)
    ↓ HTTP Requests (JSON)
ASP.NET CORE MINIMAL API
    ├─ Authentication (JWT)
    ├─ Endpoints (/books, /authors, /auth)
    ├─ Validation (Data Annotations)
    └─ Entity Framework Core
        ↓ SQL
POSTGRESQL DATABASE (Docker)
    ├─ Users table
    ├─ Books table
    └─ Authors table

The tech stack used is something you’ll also find in the software industry:

ASP.NET Core 8
PostgreSQL 16
Entity Framework Core
JWT
xUnit
Docker Compose

Prerequisites

C# basics (classes, methods, LINQ)
HTTP basics (GET, POST, PUT, DELETE)
JSON format
Command line basics

No prior experience with databases, Docker, or APIs is required.

Course structure

Initial Setup

Install all required tools before starting Week 1. Takes about 30–60 minutes.

Week 1–2: Minimal APIs Basics

Build a Books API with in-memory storage. Learn endpoints, routing, status codes, and Swagger.

Deliverable: CRUD API running locally in Swagger
Key skills: app.MapGet(), Results helper, route parameters

Week 3–4: Database with PostgreSQL

Replace the in-memory list with a real PostgreSQL database running in Docker.

Deliverable: Books API backed by PostgreSQL with an Authors table
Key skills: Docker, DbContext, EF Core migrations, one-to-many relationships

Week 5: Validation & Pagination

Add Data Annotations to entities. Optionally complete validation error responses and pagination now, or defer them to the extension page before the capstone.

Mandatory core: Data Annotations on all entities (1–2 hours)
Extension (now or later): Structured validation responses, pagination with Skip()/Take()
Key skills: Data Annotations, Results.ValidationProblem(), query parameters

Extension: Validation & Pagination

Standalone page covering validation error responses and pagination. Complete this before starting the capstone if it was deferred in Week 5.

Week 6: Authentication with JWT

Add user registration and login. Protect write endpoints so only logged-in users can use them.

Deliverable: Users can register and login; write endpoints require a JWT token
Key skills: BCrypt, JWT generation, .RequireAuthorization()

Week 7: Testing & Code Organization

Write integration tests using WebApplicationFactory and an in-memory database.

Deliverable: Test project with 5–8 passing integration tests
Key skills: xUnit, WebApplicationFactory, in-memory database, HttpClient testing

Week 8: Docker & Documentation

Containerize the full application so it starts with a single command.

Deliverable: docker-compose up runs everything; Swagger has descriptions
Key skills: Dockerfile, docker-compose.yml, Swagger descriptions

Capstone Project

Build a complete API from scratch applying all course skills. Choose from Blog API, Task Tracker, or Recipe App.

Deliverable: Working API with authentication, tests, and Docker deployment
Minimum: 3 entities, user authentication, 5 passing tests, runs in Docker

Advanced Topics

What to learn after completing the course. Includes code organization, advanced auth, complex databases, production features, and DevOps.

Priority summary

Priority	Skills
Must know	Minimal API endpoints, PostgreSQL in Docker, EF Core CRUD, JWT auth, Docker Compose
Should know	Data validation, pagination, basic testing, one-to-many relationships, Swagger
Nice to know	Code organization, logging, search and filter
Learn later	Roles and policies, unit testing with Moq, performance, production deployment