5.2 The question and what it is asked about

The question is a type, so the chain can name it and Trax can key its answers by it. Its words go on the type, once: a model reads them, and so does anyone reading the record later.

By the end of the chapter the new files are:

Shopfront/
├── Extensions/
│   └── ShopfrontServiceCollectionExtensions.cs
├── Fraud/
│   ├── LooksFraudulent.cs
│   ├── OrderRisk.cs
│   ├── FraudRules.cs
│   ├── ICandidateFraudDecider.cs
│   └── StricterFraudRules.cs
└── Trains/PlaceOrder/Junctions/
    ├── AssessRiskJunction.cs
    └── RefuseOrderJunction.cs

Fraud is the shop's policy rather than one train's, so it gets a folder outside Trains/, like the catalogue.

Fraud/LooksFraudulent.cs:

using Trax.Core.Decisions;
 
namespace Shopfront.Fraud;
 
[Asks(
    "Does this order look like a stolen card being used?",
    Yes = "Hold it: it matches how stolen cards are used.",
    No = "Take it: nothing about it is unusual."
)]
public sealed class LooksFraudulent;

A decider is asked about one value in Memory. The cart and the input together hold too much, and not the one thing that matters most: whether this customer has ordered before. A value of its own says exactly what the question is about.

Fraud/OrderRisk.cs:

namespace Shopfront.Fraud;
 
public record OrderRisk(string CustomerId, decimal Total, bool FirstOrder);

A junction gathers it.

Trains/PlaceOrder/Junctions/AssessRiskJunction.cs:

using Microsoft.EntityFrameworkCore;
using Shopfront.Data;
using Shopfront.Fraud;
using Shopfront.Trains.PlaceOrder.Models;
using Trax.Effect.Services.EffectJunction;
 
namespace Shopfront.Trains.PlaceOrder.Junctions;
 
internal class AssessRiskJunction(IShopfrontDbContext db)
    : EffectJunction<(PlaceOrderInput Order, PricedCart Cart), OrderRisk>
{
    public override async Task<OrderRisk> Run((PlaceOrderInput Order, PricedCart Cart) input)
    {
        var ordered = await db.Orders.AnyAsync(
            o => o.CustomerId == input.Order.CustomerId,
            CancellationToken
        );
        return new OrderRisk(input.Order.CustomerId, input.Cart.Total, FirstOrder: !ordered);
    }
}

SDK Reference

Gate | Decide | AddDecisionRecording | Write a decider | Try a decider in shadow | Test a train's decisions

Next: 5.3 The tracks