EF Core Repository Pattern and Unit of Work

Introduction

The Repository + Unit of Work pattern wraps EF Core behind interfaces so ShopNest's shopping cart logic is testable with mocks and controllers stay thin. Teams debate whether it's essential — this lesson shows both sides with a working cart.

After this article you will

• Implement IRepository<T> and specific repositories
• Coordinate saves with IUnitOfWork
• Register repositories in DI
• Unit test CartService with mocked IProductRepository
• Evaluate repository vs direct DbContext trade-offs

Prerequisites

• Article 18 — EF Core Fluent API
• ShopNest DbContext with Products/Orders from Articles 13–15
• SQL Server or LocalDB configured

Concept deep-dive

public interface IRepository<T> where T : class
{
    Task<T?> GetByIdAsync(int id, CancellationToken ct = default);
    Task AddAsync(T entity, CancellationToken ct = default);
    void Update(T entity);
    void Remove(T entity);
}

public interface IUnitOfWork : IAsyncDisposable
{
    IProductRepository Products { get; }
    ICartRepository Carts { get; }
    Task<int> SaveChangesAsync(CancellationToken ct = default);
}

public class UnitOfWork : IUnitOfWork
{
    private readonly ShopNestDbContext _db;
    public UnitOfWork(ShopNestDbContext db) => _db = db;
    public IProductRepository Products => new ProductRepository(_db);
    public ICartRepository Carts => new CartRepository(_db);
    public Task<int> SaveChangesAsync(CancellationToken ct = default)
        => _db.SaveChangesAsync(ct);
}

Hands-on — ShopNest Online Shopping Cart

1. ICartRepository with GetOrCreateCartAsync(userId).
2. CartService.AddItemAsync — uses IUnitOfWork, not DbContext directly.
3. xUnit test: mock IProductRepository returns product; verify AddAsync called.
4. Register: services.AddScoped<IUnitOfWork, UnitOfWork>();

Common errors & best practices

• Repository wrapping every DbSet with no added value — prefer specific repos with domain queries.
• Singleton UnitOfWork — must be Scoped per request.

Interview questions

Q: Is Repository an antipattern over EF?
A: Generic repo over DbSet adds little; specific repos with domain queries still help testability in large teams.

Q: Unit of Work purpose?
A: Single SaveChanges across multiple repos in one transaction boundary.

Summary

• Repository abstracts data access for testability
• Unit of Work shares one DbContext per request
• Shopping cart demo ties products, cart lines, SaveChanges
• Skip generic repo if team prefers DbContext + mock in tests

Previous: EF Core Fluent API
Next: EF Core Performance Optimization

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