Delete one record

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 Basic1_DeleteOneRecord().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>
/// The smallest delete: one record, in three scenarios. The usual way first (the id CreateAsync returned), then a text
/// id, then the entity itself.
/// </summary>
public sealed class Basic1_DeleteOneRecord : ISample
{
    public string Name => "delete-basics-1-delete-one-record";

    public string Title => "Delete one record";

    public async Task RunAsync(SampleContext dbContext)
    {
        await Scenario1_ByTheIdCreateReturnedAsync(dbContext.ConnectionString);

        await Scenario2_ATextIdAsync(dbContext.ConnectionString);

        await Scenario3_TheEntityItselfAsync(dbContext.ConnectionString);
    }

    private static ArxPgDbService Service(string connectionString) => new ArxPgDbService(connectionString, ArxSchemaCatalog.Create()
        .Table("account", ArxIdColumn.Generated<long>("id"))
        .Table("country", ArxIdColumn.Supplied<string>("code"))
        .Build());

    /// <summary>1. The usual way: the table and the id. True when a record was deleted.</summary>
    private static async Task Scenario1_ByTheIdCreateReturnedAsync(string connectionString)
    {
        Step("1. By the id Create returned");

        var service = Service(connectionString);

        var account = new ArxEntity("account");
        account["name"] = "Temporary account";
        account["account_number"] = "ACC-D101";
        ArxRecordId id = await service.CreateAsync(account);

        bool deleted = await service.DeleteAsync("account", id);

        Show($"deleted = {deleted}");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * SELECT count(*)
         * FROM account
         * WHERE account_number = 'ACC-D101';
         * -- Expect: 0.
         * ===========================================================
         */
    }

    /// <summary>2. A text id: delete a country by its code.</summary>
    private static async Task Scenario2_ATextIdAsync(string connectionString)
    {
        Step("2. A text id");

        var service = Service(connectionString);

        var finland = new ArxEntity("country");
        finland["code"] = "FI";
        finland["name"] = "Finland";
        await service.CreateAsync(finland);

        bool deleted = await service.DeleteAsync("country", "FI");

        Show($"country FI deleted = {deleted}");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * SELECT count(*)
         * FROM country
         * WHERE code = 'FI';
         * -- Expect: 0.
         * ===========================================================
         */
    }

    /// <summary>
    /// 3. The entity itself: an entity you created (or read) carries its id, so you can pass it back to delete it.
    /// The row is found by the table's declared id only ("id" in the schema above), never by the other attributes.
    /// </summary>
    private static async Task Scenario3_TheEntityItselfAsync(string connectionString)
    {
        Step("3. The entity itself");

        var service = Service(connectionString);

        var account = new ArxEntity("account");
        account["name"] = "Another temporary account";
        account["account_number"] = "ACC-D103";
        await service.CreateAsync(account); // sets account.RecordId to the new row's id

        // Finds the row by account.RecordId: DELETE FROM account WHERE id = <that id>.
        // "name" and "account_number" are not part of the match and are ignored: no other account is deleted because
        // it has the same name or number, and account_number is not a key (it isn't declared as one in the schema).
        // To delete by account_number instead, ask for it: new ArxDeleteOptions { Match = ArxMatch.Columns("account_number") }
        // (see Basic3_HowToFindTheRows on this page).
        int deleted = await service.DeleteAsync(account);

        Show($"{deleted} row deleted");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * SELECT count(*)
         * FROM account
         * WHERE account_number = 'ACC-D103';
         * -- Expect: 0 (the account created above is gone).
         * -- account_number is used here only to find the row by hand, since you don't know its generated id;
         * -- the delete itself matched on id.
         * ===========================================================
         */
    }
}

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. By the id Create returned
      deleted = True
  > 2. A text id
      country FI deleted = True
  > 3. The entity itself
      1 row deleted