Nothing to delete is not an error

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

using ArxSamples.PostgreSql;
using ArxSamples.PostgreSql.Operations.Delete.Basics;

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

await new Basic2_NothingToDelete().RunAsync(new SampleContext(connectionString));

The sample, as it is in the repository.

using ARX.SDK.PostgreSql.Services;
using ARX.SDK.Services;

using static ArxSamples.PostgreSql.SampleOutput;

namespace ArxSamples.PostgreSql.Operations.Delete.Basics;

/// <summary>
/// Deleting something that is already gone is a normal outcome, not an error (a retry, or two users at once). Two
/// scenarios: one record (false), and a list (0).
/// </summary>
public sealed class Basic2_NothingToDelete : ISample
{
    public string Name => "delete-basics-2-nothing-to-delete";

    public string Title => "Nothing to delete is not an error";

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

        await Scenario1_OneRecordAsync(service);

        await Scenario2_AListAsync(service);
    }

    /// <summary>1. Delete twice: the second call returns false, so a retry is safe.</summary>
    private static async Task Scenario1_OneRecordAsync(ArxPgDbService service)
    {
        Step("1. One record");

        var account = new ArxEntity("account");
        account["name"] = "Deleted twice";
        account["account_number"] = "ACC-D301";
        var id = await service.CreateAsync(account);

        var first = await service.DeleteAsync("account", id);
        var second = await service.DeleteAsync("account", id);

        Show($"first {first}, then {second}");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * SELECT count(*)
         * FROM account
         * WHERE account_number = 'ACC-D301';
         * -- Expect: 0.
         * ===========================================================
         */
    }

    /// <summary>2. A list of ids none of which exists: 0. An empty list is 0 too, without touching the database.</summary>
    private static async Task Scenario2_AListAsync(ArxPgDbService service)
    {
        Step("2. A list");

        var none = await service.DeleteMultipleAsync("account", new List<long> { 999_999_994, 999_999_993 });
        var empty = await service.DeleteMultipleAsync("account", new List<long>());

        Show($"{none} deleted, empty list {empty}");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * SELECT count(*)
         * FROM account
         * WHERE id IN (999999994, 999999993);
         * -- Expect: 0.
         * ===========================================================
         */
    }
}

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

namespace ArxSamples.PostgreSql;

/// <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 Npgsql 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.PostgreSql;

/// <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
      first True, then False
  > 2. A list
      0 deleted, empty list 0