Why should you care?

ShopNest CreateOrder requests have many optional fields — telescoping constructors get ugly fast.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public sealed class OrderDraft
{
    public string CustomerId { get; init; } = "";
    public List<string> Skus { get; init; } = new();
    public string Coupon { get; init; } = "";
}
public sealed class OrderDraftBuilder
{
    private string _customer = "";
    private readonly List<string> _skus = new();
    private string _coupon = "";
    public OrderDraftBuilder ForCustomer(string id) { _customer = id; return this; }
    public OrderDraftBuilder AddSku(string sku) { _skus.Add(sku); return this; }
    public OrderDraftBuilder WithCoupon(string c) { _coupon = c; return this; }
    public OrderDraft Build()
    {
        if (string.IsNullOrWhiteSpace(_customer) || _skus.Count == 0)
            throw new InvalidOperationException("Customer and SKUs required");
        return new OrderDraft { CustomerId = _customer, Skus = _skus.ToList(), Coupon = _coupon };
    }
}

var order = new OrderDraftBuilder().ForCustomer("u1").AddSku("HD-100").Build();
Console.WriteLine($"{order.CustomerId}: {order.Skus[0]}");

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Fluent steps gather state; Build validates.
• Callers never see a half-built order.
• C# records + with-expressions are alternatives for simpler cases.

Practice next

1. Build a valid draft and print it.
2. Omit customer and confirm Build throws.
3. Chain two AddSku calls.
4. Add WithNotes(string).
5. Return immutable copy of Skus only.

Remember

Stepwise construction. Validate at Build. Readable fluent APIs.

ShopNest order draft builder

API maps JSON into a builder then Build().

Outcome: Invalid carts fail before hitting payment.