Why should you care?

ShopNest Product.IsEligibleForDiscount() belongs in Domain — not in DbContext or controller — persistence ignorance keeps model pure.

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
{
    public int Id { get; private set; }
    public int CustomerId { get; private set; }
    private readonly List<OrderItem> _items = new();
    public IReadOnlyCollection<OrderItem> Items => _items;

    public void AddItem(Product product, int qty)
    {
        if (qty <= 0) throw new DomainException("Quantity must be positive.");
        if (product.StockQty < qty) throw new DomainException("Insufficient stock.");
        _items.Add(new OrderItem(product.Id, qty, product.Price));
    }
}

What happened?

• Order encapsulates invariants in AddItem.
• Private setter and backing list prevent invalid states.
• EF maps via Fluent API ignoring domain methods.

Practice next

1. Remove EF attributes from Domain entities if using Fluent exclusively.
2. Use factory methods and behavior methods not public setters everywhere.
3. Raise domain events on state changes if adopting DDD events.
4. Add Money value object for Price instead of raw decimal.
5. Configure backing field _items in Fluent for Order.Items mapping.

Remember

Domain encodes business rules. No EF dependency in Domain project. Infrastructure maps private setters via Fluent.

ShopNest rich order model

AddItem enforces stock rules before EF ever sees OrderItem rows.

Outcome: Invalid orders fail in domain tests without database.