Why should you care?

ShopNest Order aggregate root controls OrderItems — external code should not Add OrderItem directly bypassing Order.AddItem rules.

See it live — copy this example

Paste into a .NET project with EF Core packages, then run with LocalDB/SQL Server (dotnet ef / dotnet run).

public class Order // aggregate root
{
    public int Id { get; private set; }
    private readonly List<OrderItem> _items = new();
    public IReadOnlyCollection<OrderItem> Items => _items;

    public static Order Create(int customerId) => new() { CustomerId = customerId };

    public void AddLine(Product product, int qty) { /* invariants */ }
}

// Repository loads/saves whole aggregate
public interface IOrderRepository
{
    Task<Order?> GetByIdAsync(int id, CancellationToken ct);
    Task AddAsync(Order order, CancellationToken ct);
}

What happened?

• Order is aggregate root — only entry for modifications.
• Repository persists entire aggregate graph.
• EF Include loads items with order as one consistency unit.

Practice next

1. Identify aggregate roots: Order, Product (catalog), Customer.
2. Route changes through root methods not direct DbSet on children.
3. Size aggregates small — large aggregates hurt concurrency.
4. Map Address as owned type on Order aggregate.
5. Raise OrderPlaced domain event inside Order before SaveChanges.

Remember

Aggregate root enforces invariants. Repository per aggregate not per table. EF maps aggregates to tables with relationships.

ShopNest order aggregate

Checkout loads Order aggregate, calls AddLine for each cart row, saves once.

Outcome: Business invariants enforced before EF persists graph.