Your portfolio project: a tested Web API with EF Core

Why one strong project?

Recruiters see hundreds of CVs that list "C#, .NET, SQL". A link to a clean GitHub repository with a working API, tests and a good README proves you can actually build. In interviews it also gives you something concrete to talk about, which is easier and more convincing than abstract questions.

Pick a problem you understand

• Clinic appointments: doctors, time slots, bookings, no double-booking (409 Conflict).
• Library: books, members, issue and return, late fees.
• Hostel mess: students, monthly bills, payments, dues report.
• Small shop inventory: products, stock, sales, low-stock report.

Choose one with a few real rules (fees, limits, conflicts). Rules give you something meaningful to test and talk about.

Feature checklist

A sensible structure

ClinicBooking/
  ClinicBooking.sln
  src/
    ClinicBooking.Api/          Program.cs, endpoints, DTOs
    ClinicBooking.Core/         entities, rules (BookingService), interfaces
    ClinicBooking.Data/         ClinicDb (DbContext), migrations
  tests/
    ClinicBooking.Tests/        rule tests with fakes
  README.md
  .gitignore

A rule worth testing

public class BookingService(IAppointmentStore store, TimeProvider time)
{
    public async Task<BookingResult> BookAsync(int doctorId, DateTime slot, string patient)
    {
        if (slot <= time.GetLocalNow().DateTime)
            return BookingResult.Fail("Slot is in the past");
        if (slot.Minute % 15 != 0)
            return BookingResult.Fail("Slots start every 15 minutes");
        if (await store.IsTakenAsync(doctorId, slot))
            return BookingResult.Conflict("Slot already booked");

        await store.AddAsync(doctorId, slot, patient);
        return BookingResult.Ok();
    }
}

Plan it in weeks

1. Week 1: design the entities and endpoints on paper; create the solution; build the API with an in-memory list.
2. Week 2: add EF Core with SQLite, migrations, relationships and validation.
3. Week 3: move rules into services, write unit tests, add a global error handler.
4. Week 4: polish: README, example .http requests, clean commits; optional JWT auth or Docker.

The README that gets read

• One paragraph: what problem it solves and for whom.
• Tech used: .NET version, ASP.NET Core, EF Core, xUnit.
• How to run: clone, dotnet ef database update, dotnet run, and where to send requests.
• Example requests and responses.
• Design notes: why you chose the structure, what you would add next.

Common mistakes and fixes

• Copying a tutorial project as-is: interviewers recognise them. Change the domain and add your own rules.
• One giant commit at the end: commit in small steps with clear messages. It shows how you work.
• No tests: even ten good unit tests set you apart from most fresher projects.
• Overbuilding (microservices, five design patterns) before the basics work: finish a simple version first.