The sample application

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}");
}

The application's ARX service and its schema catalog, created once and shared by the samples.

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

namespace ArxSamples.PostgreSql;

/// <summary>The application's ARX service and its schema catalog, shared by the real and advanced samples.</summary>
public sealed partial class SampleContext
{
    private ArxSchemaCatalog? _catalog;
    private ArxPgDbService? _service;

    /// <summary>The application's schema catalog: table ids, keys and selection sets (SampleCatalog.cs).</summary>
    public ArxSchemaCatalog Catalog => _catalog ??= SampleCatalog.Build();

    /// <summary>
    /// One service for the whole application. It holds no connection: every call opens one from the Npgsql pool and
    /// closes it, unless you pass your own connection or transaction.
    /// </summary>
    public ArxPgDbService Service => _service ??= new ArxPgDbService(ConnectionString, Catalog);
}

The application's schema catalog: every table's id column and keys, and its selection sets.

using ARX.SDK.Services;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace ArxSamples.PostgreSql;

/// <summary>An account's industry. Stored in account.industry (smallint) as the enum's number.</summary>
public enum Industry : short
{
    Retail = 1,
    Manufacturing = 2,
    Healthcare = 3,
    Finance = 4,
    Technology = 5
}

/// <summary>
/// The application's schema catalog: every table's id column and keys, and every picklist (selection set),
/// defined once.
/// </summary>
/// <remarks>
/// <para>
/// <b>Ids.</b> Every table the application writes is declared with its one id column: its name, its .NET type, and
/// whether the database generates it (<c>ArxIdColumn.Generated</c>: identity, sequence, default) or the caller supplies
/// it (<c>ArxIdColumn.Supplied</c>: a natural id, a client-generated Guid). A table with no id column, such as a log or a
/// table identified by several columns together, is declared <c>ArxIdColumn.NoIdColumn</c>. ARX never reads ids from
/// the database: the developer knows the schema, and an undeclared table is refused (ARX1016).
/// </para>
/// <para>
/// <b>Keys.</b> Optional business keys: one or more columns whose values identify a record, such as an account number,
/// or a region and a SKU together. Create doesn't use them (the database's unique constraints do the enforcing); Update
/// and Delete will be able to find rows by them. <c>ValidateSchemaAsync</c> checks ids and keys against the database
/// when you ask it to.
/// </para>
/// <para>
/// <b>Selection sets.</b> /// A selection set (picklist, option set) is a column that only accepts a fixed list of codes, each with a display
/// text: an account's status (ACTIVE, ON_HOLD, CLOSED), a contact's preferred channel (E, P, S). The catalog tells ARX,
/// for each set:
/// </para>
/// <list type="bullet">
/// <item><b>Name</b>: what an <see cref="ArxSelectionSetValue"/> refers to, for example <c>new ArxSelectionSetValue("AccountStatus", "ON_HOLD")</c>.</item>
/// <item><b>Kind</b>: what the codes are, matching the column: Integer, String, Character, Boolean, Decimal, Guid, or a
/// PostgreSQL enum type (DatabaseEnum).</item>
/// <item><b>Multiplicity</b>: Single (one code), or several codes stored as an array (Array), bit flags (Flags), a
/// delimited string (Delimited) or a JSON array (Json).</item>
/// <item><b>Options</b>: each code with its display text and order. A retired option (<c>IsActive: false</c>) stays
/// readable in old rows, but can't be written any more.</item>
/// </list>
/// <para>
/// Build the catalog once at startup and give it to the service: <c>new ArxPgDbService(connectionString, SampleCatalog.Build())</c>.
/// ARX checks every <see cref="ArxSelectionSetValue"/> against it in memory, before any SQL is sent, and stores the code
/// itself in the column: no lookup table, no extra query. A plain value (a string or number that isn't an
/// ArxSelectionSetValue) isn't checked.
/// </para>
/// <para>
/// The catalog is plain code, so the options can come from wherever you keep them: written out here, taken from a .NET
/// enum (<c>AddEnum</c>), loaded from JSON (<see cref="SetsJson"/> and <see cref="FromJson"/> below), or loaded at
/// startup from your own option table and passed to <c>new ArxSelectionSetDefinition(name, kind, options)</c>. ARX
/// never reads option tables or files itself.
/// </para>
/// </remarks>
public static class SampleCatalog
{
    /// <summary>
    /// Selection sets kept as JSON, as an application might keep them in a file, a settings store or a database column.
    /// Here the JSON is in the class itself; in an application, read it from wherever you keep it
    /// (<c>File.ReadAllText("selection-sets.json")</c>, configuration, an HTTP call) and pass it to <see cref="FromJson"/>.
    /// "multiplicity" and "active" are optional (Single and true).
    /// </summary>
    public const string SetsJson = """
        [
          {
            "name": "LeadSource",
            "kind": "String",
            "options": [
              { "value": "WEB",       "text": "Website",    "order": 0 },
              { "value": "REFERRAL",  "text": "Referral",   "order": 1 },
              { "value": "EVENT",     "text": "Trade show", "order": 2 },
              { "value": "COLD_CALL", "text": "Cold call",  "order": 3, "active": false }
            ]
          },
          {
            "name": "ContactRating",
            "kind": "Integer",
            "multiplicity": "Single",
            "options": [
              { "value": 1, "text": "Poor" },
              { "value": 2, "text": "Fair" },
              { "value": 3, "text": "Good" },
              { "value": 4, "text": "Very good" },
              { "value": 5, "text": "Excellent" }
            ]
          }
        ]
        """;

    public static ArxSchemaCatalog Build()
    {
        var builder = ArxSchemaCatalog.Create()

            // ---------- tables: id column and keys ----------
            // Generated bigint ids (bigserial): the database fills them in. The keys are the unique columns that also
            // identify a record.
            .Table("account", ArxIdColumn.Generated<long>("id")).Key("account", "account_number")
            .Table("contact", ArxIdColumn.Generated<long>("id")).Key("contact", "email")

            // Retrieve: a contact's account_id reads back as a reference to its account, named by the account's
            // name; a contact is named by its first and last names.
            .Lookup("contact", "account_id", "account")
            .DisplayName("account", "name")
            .DisplayName("contact", new[] { "first_name", "last_name" }, " ")

            .Table("product_category", ArxIdColumn.Generated<long>("id")).Key("product_category", "name")
            .Table("product", ArxIdColumn.Generated<long>("id")).Key("product", "sku")
            .Table("sales_order", ArxIdColumn.Generated<long>("id")).Key("sales_order", "order_number")
            .Table("order_line", ArxIdColumn.Generated<long>("id"))
            .Table("data_type_showcase", ArxIdColumn.Generated<long>("id"))

            // A natural id: the caller gives the ISO country code.
            .Table("country", ArxIdColumn.Supplied<string>("code"))

            // A generated uuid id (DEFAULT gen_random_uuid()).
            .Table("device", ArxIdColumn.Generated<Guid>("id")).Key("device", "serial_number")

            // No id column: a price is identified by its region and SKU together, a compound key.
            .Table("price_list", ArxIdColumn.NoIdColumn).Key("price_list", "region", "sku")

            // No primary key at all: the same action can be logged twice.
            .Table("activity_log", ArxIdColumn.NoIdColumn)

            // A partitioned table without an id: a visit is a fact, never updated (Retrieve Advanced8).
            .Table("web_visit", ArxIdColumn.NoIdColumn)

            // ---------- selection sets ----------

            // From a .NET enum: the set is named after the enum ("Industry"), the codes are its numbers (Retail = 1, …),
            // the display texts are its member names. Column: account.industry smallint.
            .AddEnum<Industry>()

            // Written out: String codes with display texts, single choice. Column: account.status text.
            .Add("AccountStatus", ArxSelectionSetKind.String, ("ACTIVE", "Active"), ("ON_HOLD", "On hold"), ("CLOSED", "Closed"))

            // Multiple choice, stored as an array of codes. RESELLER is retired: rows that have it still read back,
            // but new writes can't use it. Column: account.segments text[].
            .Add(new ArxSelectionSetDefinition("CustomerSegment", ArxSelectionSetKind.String, new[]
            {
                new ArxSelectionSetOption("SMB", "Small business", 0),
                new ArxSelectionSetOption("ENTERPRISE", "Enterprise", 1),
                new ArxSelectionSetOption("PUBLIC", "Public sector", 2),
                new ArxSelectionSetOption("RESELLER", "Reseller", 3, IsActive: false)
            }, ArxSelectionSetMultiplicity.Array))

            // Single-character codes. Column: contact.preferred_channel char(1).
            .Add("ContactChannel", ArxSelectionSetKind.Character, ('E', "Email"), ('P', "Phone"), ('S', "Text message"))

            // The labels of a PostgreSQL enum type: the value is written with a cast to that type.
            // Column: data_type_showcase.mood showcase_mood.
            .Add(new ArxSelectionSetDefinition("Mood", ArxSelectionSetKind.DatabaseEnum, new[]
            {
                new ArxSelectionSetOption("happy", "Happy", 0),
                new ArxSelectionSetOption("neutral", "Neutral", 1),
                new ArxSelectionSetOption("sad", "Sad", 2)
            }, databaseTypeName: "showcase_mood"));

        // Loaded from JSON: LeadSource (contact.lead_source text) and ContactRating (contact.rating smallint).
        foreach (var set in FromJson(SetsJson))
        {
            builder.Add(set);
        }

        return builder.Build();
    }

    /// <summary>Reads selection set definitions from JSON (the shape of <see cref="SetsJson"/>).</summary>
    public static IEnumerable<ArxSelectionSetDefinition> FromJson(string json)
    {
        var options = new JsonSerializerOptions
        {
            PropertyNameCaseInsensitive = true,
            Converters = { new JsonStringEnumConverter() }   // "String", "Integer", "Array", … as names
        };

        var sets = JsonSerializer.Deserialize<List<JsonSet>>(json, options)
            ?? throw new InvalidOperationException("The selection set JSON is empty.");

        foreach (var set in sets)
        {
            yield return new ArxSelectionSetDefinition(
                set.Name,
                set.Kind,
                set.Options.Select(x => new ArxSelectionSetOption(Code(x.Value, set.Kind), x.Text, x.Order, x.Active)),
                set.Multiplicity,
                set.DatabaseTypeName);
        }
    }

    /// <summary>A JSON value as a code of the set's kind: JSON has no char, Guid or 64-bit integer of its own.</summary>
    private static object Code(JsonElement value, ArxSelectionSetKind kind) => kind switch
    {
        ArxSelectionSetKind.Integer => value.GetInt64(),
        ArxSelectionSetKind.Decimal => value.GetDecimal(),
        ArxSelectionSetKind.Boolean => value.GetBoolean(),
        ArxSelectionSetKind.Guid => value.GetGuid(),
        ArxSelectionSetKind.Character => value.GetString()![0],
        _ => value.GetString()!   // String and DatabaseEnum
    };

    private sealed record JsonSet(
        string Name,
        ArxSelectionSetKind Kind,
        List<JsonOption> Options,
        ArxSelectionSetMultiplicity Multiplicity = ArxSelectionSetMultiplicity.Single,
        string? DatabaseTypeName = null);

    private sealed record JsonOption(JsonElement Value, string Text, int Order = 0, bool Active = true);
}

The plain Npgsql read-back helper, for the samples that show what PostgreSQL stored.

namespace ArxSamples.PostgreSql;

/// <summary>Plain Npgsql outside the SDK, for the samples that show what PostgreSQL stored.</summary>
public sealed partial class SampleContext
{
    private PGDirectHelper? _direct;

    /// <summary>Plain Npgsql outside the SDK, used only to reset the tables and to show what was stored.</summary>
    public PGDirectHelper Direct => _direct ??= new PGDirectHelper(ConnectionString);
}

Plain Npgsql, not part of ARX: reads rows back so a sample can show what PostgreSQL stored.

using ARX.SDK.Services;
using Npgsql;

namespace ArxSamples.PostgreSql;

/// <summary>
/// Plain Npgsql, outside ARX.SDK: resets the sample tables, reads rows back so a sample can show what PostgreSQL
/// actually stored (printing is SampleOutput.cs). It isn't part of the SDK and isn't how an application uses ARX;
/// it only lets the samples verify and show their results. Reading through ARX (Retrieve, RetrieveMultiple) gets its
/// own samples once those operations are hardened.
/// </summary>
public sealed class PGDirectHelper
{
    private readonly string _connectionString;

    public PGDirectHelper(string connectionString)
    {
        _connectionString = connectionString;
    }

    /// <summary>The same helper pointed at another database on the same server.</summary>
    public PGDirectHelper ForDatabase(string database)
        => new PGDirectHelper(new NpgsqlConnectionStringBuilder(_connectionString) { Database = database }.ConnectionString);

    /// <summary>The connection string of <see cref="ForDatabase"/>'s database, for a second ARX service.</summary>
    public string ConnectionStringFor(string database)
        => new NpgsqlConnectionStringBuilder(_connectionString) { Database = database }.ConnectionString;

    /// <summary>Creates <paramref name="database"/> on the server if it doesn't exist yet (setup for the two-database sample).</summary>
    public async Task EnsureDatabaseExistsAsync(string database)
    {
        await using var connection = await OpenConnectionAsync();

        await using (var exists = new NpgsqlCommand("SELECT count(*) FROM pg_database WHERE datname = $1", connection))
        {
            exists.Parameters.Add(new NpgsqlParameter { Value = database });

            if ((long)(await exists.ExecuteScalarAsync())! > 0)
            {
                return;
            }
        }

        // CREATE DATABASE takes no parameters; the name is the sample's own constant, quoted.
        await using var create = new NpgsqlCommand($"CREATE DATABASE \"{database.Replace("\"", "\"\"")}\"", connection);
        await create.ExecuteNonQueryAsync();
    }

    /// <summary>Drops and recreates the sample tables (Schema/sample-schema.sql).</summary>
    public async Task ResetSchemaAsync()
    {
        var sql = await File.ReadAllTextAsync(Path.Combine(AppContext.BaseDirectory, "Schema", "sample-schema.sql"));
        await ExecuteAsync(sql);
    }

    public async Task ExecuteAsync(string sql)
    {
        await using var connection = await OpenConnectionAsync();
        await using var command = new NpgsqlCommand(sql, connection);
        await command.ExecuteNonQueryAsync();
    }

    public async Task<NpgsqlConnection> OpenConnectionAsync()
    {
        var connection = new NpgsqlConnection(_connectionString);
        await connection.OpenAsync();
        return connection;
    }

    /// <summary>Counts rows, optionally with a WHERE clause using $1, $2, … for <paramref name="parameters"/>.</summary>
    public async Task<long> CountAsync(string table, string where = "true", params object[] parameters)
    {
        await using var connection = await OpenConnectionAsync();
        await using var command = new NpgsqlCommand($"SELECT count(*) FROM {table} WHERE {where}", connection);

        foreach (var parameter in parameters)
        {
            command.Parameters.Add(new NpgsqlParameter { Value = parameter });
        }

        return (long)(await command.ExecuteScalarAsync())!;
    }

    /// <summary>Reads one row by id as column → value (null for SQL NULL).</summary>
    public async Task<Dictionary<string, object?>> RowAsync(string table, long id)
    {
        await using var connection = await OpenConnectionAsync();
        await using var command = new NpgsqlCommand($"SELECT * FROM {table} WHERE id = $1", connection);
        command.Parameters.Add(new NpgsqlParameter { Value = id });
        await using var reader = await command.ExecuteReaderAsync();

        if (!await reader.ReadAsync())
        {
            throw new InvalidOperationException($"No {table} row with id {id}.");
        }

        var row = new Dictionary<string, object?>(StringComparer.OrdinalIgnoreCase);

        for (var i = 0; i < reader.FieldCount; i++)
        {
            row[reader.GetName(i)] = reader.IsDBNull(i) ? null : reader.GetValue(i);
        }

        return row;
    }

    /// <summary>
    /// Reads columns of one row as PostgreSQL prints them (<c>column::text</c>, in a UTC session), which shows the stored
    /// value exactly, whatever its type.
    /// </summary>
    public async Task<Dictionary<string, string?>> TextRowAsync(string table, long id, params string[] columns)
    {
        await using var connection = await OpenConnectionAsync();
        await using (var zone = new NpgsqlCommand("SET TIME ZONE 'UTC'", connection))
        {
            await zone.ExecuteNonQueryAsync();
        }

        var select = string.Join(", ", columns.Select(x => $"{x}::text"));
        await using var command = new NpgsqlCommand($"SELECT {select} FROM {table} WHERE id = $1", connection);
        command.Parameters.Add(new NpgsqlParameter { Value = id });
        await using var reader = await command.ExecuteReaderAsync();

        if (!await reader.ReadAsync())
        {
            throw new InvalidOperationException($"No {table} row with id {id}.");
        }

        var row = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);

        for (var i = 0; i < columns.Length; i++)
        {
            row[columns[i]] = reader.IsDBNull(i) ? null : reader.GetString(i);
        }

        return row;
    }
}

A security check around ARX calls: suspected injection logged as a security event, strikes, blocking.

using ARX.SDK;

namespace ArxSamples.PostgreSql;

/// <summary>Where the names (tables, attributes, match columns) in a call come from. It decides what an ARX1017 means.</summary>
public enum NameSource
{
    /// <summary>A name built from what a user sent (a form field, a file header, a query string): ARX1017 is a suspected attack.</summary>
    UserInput,

    /// <summary>A name from your code or configuration: ARX1017 is a bug in your code, not an attack. Nobody is blocked.</summary>
    Code,
}

/// <summary>What the guard did with a call.</summary>
public enum GuardOutcome
{
    /// <summary>The call ran.</summary>
    Done,

    /// <summary>ARX refused the call with ARX1017; the event is logged and the user got a plain message.</summary>
    Refused,

    /// <summary>The user was already blocked: the call wasn't attempted.</summary>
    Blocked,
}

/// <summary>One entry of the security log: a suspected attack, or a bug when the names came from code.</summary>
public sealed record SecurityEvent(DateTimeOffset At, string User, string Action, string Kind, string Detail);

/// <summary>The outcome, the call's result when it ran, and the message to show the user (never the detection details).</summary>
public sealed record GuardResult<T>(GuardOutcome Outcome, T? Value, string ForTheUser);

/// <summary>
/// A security check around ARX calls: the pattern to copy into an application, kept small so it can be read in one
/// go. It lets every ARX error through except <c>ARX1017 SuspectedInjection</c>, which it turns into:
/// <list type="bullet">
/// <item>an entry in the security log (<see cref="Events"/>), with the user, the action and ARX's message (the name is
/// escaped and cut to 64 characters by ARX, so it is safe to log);</item>
/// <item>a plain message for the user that doesn't say what was detected;</item>
/// <item>a strike against the user. After <c>blockAfter</c> strikes the user is blocked and their calls aren't attempted.
/// One strike never blocks anyone, so a single false positive only costs one refused request;</item>
/// <item>no strike when the names came from your own code (<see cref="NameSource.Code"/>): that's a bug to fix, logged
/// as one.</item>
/// </list>
/// A false positive (a harmless name such as a file header <c>E-mail (work)</c> flagged as SQL) is handled by triage:
/// read the event, fix the mapping that let the name through, and <see cref="Unblock"/> the user if needed.
/// In a real application the log goes to your SIEM or security monitoring and the strikes live in a shared store
/// (Redis, the database), not in memory.
/// </summary>
public sealed class SecurityGuard
{
    private const string ATTACK = "suspected attack";
    private const string BUG = "bug";

    private readonly object _gate = new();
    private readonly int _blockAfter;
    private readonly Dictionary<string, int> _strikes = new(StringComparer.Ordinal);
    private readonly List<SecurityEvent> _events = new();

    public SecurityGuard(int blockAfter = 3)
    {
        _blockAfter = blockAfter;
    }

    /// <summary>The security log, oldest first.</summary>
    public IReadOnlyList<SecurityEvent> Events
    {
        get
        {
            lock (_gate)
            {
                return _events.ToArray();
            }
        }
    }

    public bool IsBlocked(string user)
    {
        lock (_gate)
        {
            return _strikes.TryGetValue(user, out var strikes) && strikes >= _blockAfter;
        }
    }

    /// <summary>After triage found the events were a false positive: clears the user's strikes (the log is kept).</summary>
    public void Unblock(string user)
    {
        lock (_gate)
        {
            _strikes.Remove(user);
        }
    }

    /// <summary>Runs <paramref name="call"/> for <paramref name="user"/> unless they are blocked, and handles ARX1017 as described above.</summary>
    public async Task<GuardResult<T>> RunAsync<T>(string user, string action, NameSource names, Func<Task<T>> call)
    {
        if (IsBlocked(user))
        {
            return new GuardResult<T>(GuardOutcome.Blocked, default, "Your access is suspended. Contact support.");
        }

        try
        {
            return new GuardResult<T>(GuardOutcome.Done, await call(), "Done.");
        }
        catch (ArxValidationException error) when (error.Code == ArxErrorCode.SuspectedInjection)
        {
            lock (_gate)
            {
                if (names == NameSource.Code)
                {
                    _events.Add(new SecurityEvent(DateTimeOffset.UtcNow, user, action, BUG, error.Message));
                    return new GuardResult<T>(GuardOutcome.Refused, default, "Something went wrong on our side. It has been reported.");
                }

                _strikes[user] = _strikes.GetValueOrDefault(user) + 1;
                _events.Add(new SecurityEvent(DateTimeOffset.UtcNow, user, action, ATTACK, error.Message));
            }

            return new GuardResult<T>(GuardOutcome.Refused, default, "The request couldn't be processed.");
        }
    }
}