Catch a record that doesn't exist

Runs the sample. Generated for this page; it reads the connection string from the environment.

using ArxSamples.MySQL;
using ArxSamples.MySQL.Operations.Update.Basics;

// The connection string comes from the environment, never from the code (see "Configure the connection").
var connectionString = Environment.GetEnvironmentVariable("ARX_SAMPLES_MYSQL")
    ?? throw new InvalidOperationException("Set the ARX_SAMPLES_MYSQL environment variable to your MySQL connection string.");

await new Basic3_RecordNotFound().RunAsync(new SampleContext(connectionString));

The sample, as it is in the repository.

using ARX.SDK;
using ARX.SDK.MySQL.Services;
using ARX.SDK.Services;

using static ArxSamples.MySQL.SampleOutput;

namespace ArxSamples.MySQL.Operations.Update.Basics;

/// <summary>
/// An update of a record that doesn't exist is an error, ARX2002 RecordNotFound, never silently nothing. Two scenarios:
/// one record, and a list where one is missing.
/// </summary>
public sealed class Basic3_RecordNotFound : ISample
{
    public string Name => "update-basics-3-record-not-found";

    public string Title => "Catch a record that doesn't exist";

    public async Task RunAsync(SampleContext dbContext)
    {
        var service = new ArxMySqlDbService(dbContext.ConnectionString, ArxSchemaCatalog.Create()
            .Table("account", ArxIdColumn.Generated<long>("id"))
            .Build());

        await Scenario1_OneRecordAsync(service);

        await Scenario2_OneOfManyAsync(service);
    }

    /// <summary>1. The usual case: the id doesn't exist (deleted meanwhile, or a wrong id).</summary>
    private static async Task Scenario1_OneRecordAsync(ArxMySqlDbService service)
    {
        Step("1. One record");

        var change = new ArxEntity("account");
        change["id"] = 999_999_998L;
        change["name"] = "Nobody";

        try
        {
            await service.UpdateAsync(change);
        }
        catch (ArxException error) when (error.Code == ArxErrorCode.RecordNotFound)
        {
            Show($"{error.Message}");
        }

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * SELECT count(*)
         * FROM account
         * WHERE name = 'Nobody';
         * -- Expect: 0.
         * ===========================================================
         */
    }

    /// <summary>2. In a list, the error says how many entities matched no row, and nothing in the list was changed.</summary>
    private static async Task Scenario2_OneOfManyAsync(ArxMySqlDbService service)
    {
        Step("2. One of many");

        var account = new ArxEntity("account");
        account["name"] = "Margie's Travel";
        account["account_number"] = "ACC-U401";
        var id = await service.CreateAsync(account);

        var real = new ArxEntity("account");
        real.RecordId = id;
        real["name"] = "Margie's Travel Agency";

        var ghost = new ArxEntity("account");
        ghost["id"] = 999_999_997L;
        ghost["name"] = "Ghost";

        try
        {
            await service.UpdateMultipleAsync(new[] { real, ghost });
        }
        catch (ArxException error) when (error.Code == ArxErrorCode.RecordNotFound)
        {
            Show($"{error.Message}");
        }

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * SELECT name
         * FROM account
         * WHERE account_number = 'ACC-U401';
         * -- Expect: 1 row, Margie's Travel: the real account wasn't renamed either.
         * ===========================================================
         */
    }
}

What every sample is given: the connection string (and the ISample interface the samples implement).

namespace ArxSamples.MySQL;

/// <summary>One documentation sample: a scenario a real application has, shown end to end.</summary>
public interface ISample
{
    /// <summary>The name to run it alone: <c>dotnet run -- &lt;name&gt;</c>.</summary>
    string Name { get; }

    /// <summary>One line on what it shows.</summary>
    string Title { get; }

    Task RunAsync(SampleContext dbContext);
}

/// <summary>
/// What a sample is given. Every sample gets the connection string; the application's service and catalog
/// (SampleContext.Application.cs) and the plain MySqlConnector read-back helper (SampleContext.Direct.cs) live in their own
/// files, so a sample needs only the files it uses.
/// </summary>
public sealed partial class SampleContext
{
    public SampleContext(string connectionString)
    {
        ConnectionString = connectionString;
    }

    public string ConnectionString { get; }
}

How the samples print: Step for each scenario, Show for what it did, ShowError for an error caught on purpose.

using ARX.SDK;

namespace ArxSamples.MySQL;

/// <summary>How the samples print: a numbered step for each scenario, then what it did.</summary>
public static class SampleOutput
{
    /// <summary>The start of a scenario: <c>Step("1. By the id Create returned")</c>.</summary>
    public static void Step(string text) => Console.WriteLine($"  > {text}");

    /// <summary>What the scenario did.</summary>
    public static void Show(string text) => Console.WriteLine($"      {text}");

    /// <summary>An ARX error the scenario caught on purpose.</summary>
    public static void ShowError(ArxException exception)
        => Console.WriteLine($"      caught {exception.GetType().Name}: {exception.Message}");
}

  > 1. One record
      ARX2002 RecordNotFound: Update of 'account': no row matched the id (column id). Nothing was changed.
  > 2. One of many
      ARX2002 RecordNotFound: UpdateMultiple on 'account': 1 of 2 entities matched no row. Nothing was changed.