9.2 The stock report

The report is a train like any other. Its output is the report: the time it was taken and each product's stock. The run's record keeps that output, so the report needs no table of its own.

By the end of the chapter the new trains are:

Trains/
├── StockReport/
│   ├── StockReportInput.cs
│   ├── StockReportOutput.cs
│   ├── IStockReportTrain.cs
│   ├── StockReportTrain.cs
│   ├── Junctions/
│   │   └── CountStockJunction.cs
│   └── Models/
│       └── StockLine.cs
└── LowStockCheck/
    ├── LowStockCheckInput.cs
    ├── LowStockCheckOutput.cs
    ├── ILowStockCheckTrain.cs
    ├── LowStockCheckTrain.cs
    └── Junctions/
        ├── FindLowStockJunction.cs
        └── NotifyStaffJunction.cs

A scheduled train's input is stored with its manifest, so it implements IManifestProperties, the marker Trax uses to tell an input it may store from any other object. The report needs no settings, so its input is empty.

Trains/StockReport/StockReportInput.cs:

using Trax.Effect.Models.Manifest;
 
namespace Shopfront.Trains.StockReport;
 
public record StockReportInput : IManifestProperties;

Trains/StockReport/Models/StockLine.cs:

namespace Shopfront.Trains.StockReport.Models;
 
public record StockLine(string Sku, int Stock);

StockLine is part of the output, so it is public.

Trains/StockReport/StockReportOutput.cs:

using Shopfront.Trains.StockReport.Models;
 
namespace Shopfront.Trains.StockReport;
 
public record StockReportOutput(DateTime TakenAt, int Units, List<StockLine> Lines);

Trains/StockReport/IStockReportTrain.cs:

using Trax.Effect.Services.ServiceTrain;
 
namespace Shopfront.Trains.StockReport;
 
public interface IStockReportTrain : IServiceTrain<StockReportInput, StockReportOutput>;

Trains/StockReport/Junctions/CountStockJunction.cs:

using Microsoft.EntityFrameworkCore;
using Shopfront.Data;
using Shopfront.Trains.StockReport.Models;
using Trax.Effect.Services.EffectJunction;
 
namespace Shopfront.Trains.StockReport.Junctions;
 
internal class CountStockJunction(IShopfrontDbContext db, ILogger<CountStockJunction> logger)
    : EffectJunction<StockReportInput, StockReportOutput>
{
    public override async Task<StockReportOutput> Run(StockReportInput input)
    {
        var lines = await db
            .Products.OrderBy(p => p.Sku)
            .Select(p => new StockLine(p.Sku, p.Stock))
            .ToListAsync(CancellationToken);
 
        var report = new StockReportOutput(DateTime.UtcNow, lines.Sum(l => l.Stock), lines);
        logger.LogInformation(
            "Counted {Units} units across {Products} products",
            report.Units,
            lines.Count
        );
        return report;
    }
}

Trains/StockReport/StockReportTrain.cs:

using Shopfront.Trains.StockReport.Junctions;
using Trax.Core.Functional;
using Trax.Effect.Services.ServiceTrain;
 
namespace Shopfront.Trains.StockReport;
 
public class StockReportTrain : ServiceTrain<StockReportInput, StockReportOutput>, IStockReportTrain
{
    protected override Task<Either<Exception, StockReportOutput>> Junctions() =>
        Chain<CountStockJunction>().Resolve();
}

The train carries no [TraxAuthorize] and no GraphQL attribute. Nobody asks for it: the scheduler runs it, as trusted infrastructure, and it is not part of the API.

A scheduled run has no caller. The products have no owner, so the report reads them all; a train that read orders would see none, because the query filter from chapter 6 shows a context with no caller nothing. That is the filter failing closed, and it is why the report counts products rather than adding up orders.

SDK Reference

AddScheduler | Schedule | Scheduling helpers | Exclusions | Scheduling options | Dependent trains

Next: 9.3 The low-stock check