Set up the service from the database's schema

Runs the sample. Generated for this page; it reads the connection string from the environment and first remakes the sample database from sample-schema.json.

using ArxSamples.MongoDb;
using ArxSamples.MongoDb.Operations.Create.AdvancedCases;

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

var dbContext = new SampleContext(connectionString);

// Every run starts from the sample data: this deletes and makes again what sample-schema.json lists
// (save the file in the project folder, see Get started).
await dbContext.Direct.ResetAsync();

await new Advanced3_DynamicTableSchemaServiceSetup().RunAsync(dbContext);

The sample, as it is in the repository.

using ARX.SDK;
using ARX.SDK.MongoDb.Services;
using ARX.SDK.Services;

using static ArxSamples.MongoDb.SampleOutput;

namespace ArxSamples.MongoDb.Operations.Create.AdvancedCases;

/// <summary>
/// The service set up from the database instead of by hand, in three scenarios: preload a collection at startup, create
/// through the preloaded service, and Strict, where only the preloaded fields may be written.
/// </summary>
/// <remarks>
/// <c>ArxPreLoadTable</c> reads, once, each collection's id (ObjectId ids are generated strings), its unique indexes (as
/// keys) and the field types of its <c>$jsonSchema</c> validator. A value of the wrong type is then refused before
/// anything is sent (ARX4004). MongoDB has no foreign keys: declare lookups in the configure callback.
/// </remarks>
public sealed class Advanced3_DynamicTableSchemaServiceSetup : ISample
{
    public string Name => "create-advanced-3-dynamic-table-schema-service-setup";

    public string Title => "Set up the service from the database's schema";

    public async Task RunAsync(SampleContext dbContext)
    {
        var catalog = await Scenario1_PreloadAtStartupAsync(dbContext.ConnectionString);

        await Scenario2_CreateThroughThePreloadedServiceAsync(dbContext.ConnectionString, catalog);

        await Scenario3_StrictAsync(dbContext.ConnectionString, catalog);
    }

    /// <summary>1. Preload the lead collection once, at startup.</summary>
    private static async Task<ArxSchemaCatalog> Scenario1_PreloadAtStartupAsync(string connectionString)
    {
        Step("1. Preload at startup");

        var catalog = await new ArxPreLoadTable(new ArxPreLoadTableRegister().PreLoadTable("lead")).LoadAsync(connectionString);

        catalog.TryGetTable("lead", out var lead);
        Show($"lead: id {lead.IdColumn}, keys {string.Join(", ", lead.Keys)}, fields {string.Join(", ", lead.Columns.Keys)}");

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * db.getCollectionInfos({ name: "lead" })[0].options.validator
         * -- Expect: the $jsonSchema with email, full_name, score and captured_on.
         * ===========================================================
         */
        return catalog;
    }

    /// <summary>2. Create through the preloaded service; a value of the wrong type is refused before MongoDB sees it.</summary>
    private static async Task Scenario2_CreateThroughThePreloadedServiceAsync(string connectionString, ArxSchemaCatalog catalog)
    {
        Step("2. Create through the preloaded service");

        var service = new ArxMongoDbService(connectionString, catalog);

        var lead = new ArxEntity("lead");
        lead["email"] = "lead-m701@example.com";
        lead["full_name"] = "Kim Abercrombie";
        lead["score"] = 72;
        lead["captured_on"] = new DateTime(2026, 11, 9, 8, 0, 0, DateTimeKind.Utc);
        await service.CreateAsync(lead);
        Show("created lead-m701@example.com");

        var wrong = new ArxEntity("lead");
        wrong["email"] = "lead-m702@example.com";
        wrong["score"] = "high";

        try
        {
            await service.CreateAsync(wrong);
        }
        catch (ArxValidationException exception) when (exception.Code == ArxErrorCode.DataTypeMismatch)
        {
            ShowError(exception);
        }

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * db.lead.find({ email: { $in: ["lead-m701@example.com", "lead-m702@example.com"] } })
         * -- Expect: 1 document, lead-m701@example.com with score 72.
         * ===========================================================
         */
    }

    /// <summary>3. Strict: a field the preload didn't load is refused (ARX1018), so a typo can't add a field.</summary>
    private static async Task Scenario3_StrictAsync(string connectionString, ArxSchemaCatalog catalog)
    {
        Step("3. Strict");

        var service = new ArxMongoDbService(connectionString, catalog) { Strict = true };

        var lead = new ArxEntity("lead");
        lead["email"] = "lead-m703@example.com";
        lead["scroe"] = 10;

        try
        {
            await service.CreateAsync(lead);
        }
        catch (ArxValidationException exception) when (exception.Code == ArxErrorCode.NotPreloaded)
        {
            ShowError(exception);
        }

        /* ===========================================================
         * [DIRECT QUERY CHECK]
         * -----------------------------------------------------------
         * db.lead.countDocuments({ email: "lead-m703@example.com" })
         * -- Expect: 0.
         * ===========================================================
         */
    }
}

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

namespace ArxSamples.MongoDb;

/// <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 MongoDB driver 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.MongoDb;

/// <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 plain MongoDB.Driver read-back helper, for the samples that show what MongoDB stored.

namespace ArxSamples.MongoDb;

/// <summary>The plain MongoDB driver outside the SDK, for the samples that show what MongoDB stored.</summary>
public sealed partial class SampleContext
{
    private MongoDirectHelper? _direct;

    /// <summary>The plain MongoDB driver outside the SDK, used only to reset the database and to show what was stored.</summary>
    public MongoDirectHelper Direct => _direct ??= new MongoDirectHelper(ConnectionString);
}

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

using MongoDB.Bson;
using MongoDB.Driver;

namespace ArxSamples.MongoDb;

/// <summary>
/// The plain MongoDB driver, outside the SDK: it resets the sample database from Schema/sample-schema.json and shows
/// what was stored. Samples never write through it.
/// </summary>
public sealed class MongoDirectHelper
{
    private readonly IMongoDatabase _database;

    public MongoDirectHelper(string connectionString)
    {
        var url = MongoUrl.Create(connectionString);
        _database = new MongoClient(url).GetDatabase(url.DatabaseName ?? "arx_samples");
    }

    /// <summary>
    /// The sample schema: Schema/sample-schema.json next to the program (the samples' own project), or sample-schema.json
    /// in the project folder (a sample copied from its page, as Get started says).
    /// </summary>
    private static string SchemaPath()
    {
        var candidates = new[]
        {
            Path.Combine(AppContext.BaseDirectory, "Schema", "sample-schema.json"),
            Path.Combine(Directory.GetCurrentDirectory(), "sample-schema.json"),
            Path.Combine(Directory.GetCurrentDirectory(), "Schema", "sample-schema.json")
        };

        return candidates.FirstOrDefault(File.Exists)
            ?? throw new FileNotFoundException("sample-schema.json isn't in the project folder: download it from the Get started page and save it next to Program.cs.");
    }

    /// <summary>Drops the sample database and makes its collections, indexes and validators again.</summary>
    public async Task ResetAsync()
    {
        var schema = BsonDocument.Parse(await File.ReadAllTextAsync(SchemaPath()));

        foreach (var collection in schema["collections"].AsBsonArray.Select(x => x.AsBsonDocument))
        {
            var name = collection["name"].AsString;

            // Only the collections the schema lists are dropped and made again: anything else in the database is left alone.
            await _database.DropCollectionAsync(name);
            var options = new CreateCollectionOptions<BsonDocument>();

            if (collection.TryGetValue("validator", out var validator))
            {
                options.Validator = validator.AsBsonDocument;
            }

            await _database.CreateCollectionAsync(name, options);

            foreach (var index in collection.GetValue("indexes", new BsonArray()).AsBsonArray.Select(x => x.AsBsonDocument))
            {
                var keys = index["keys"].AsBsonDocument;
                var indexOptions = new CreateIndexOptions<BsonDocument> { Unique = index.GetValue("unique", false).AsBoolean };

                if (index.GetValue("partial", false).AsBoolean)
                {
                    indexOptions.PartialFilterExpression = new BsonDocument(keys.Names.Select(x => new BsonElement(x, new BsonDocument("$exists", true))));
                }

                await _database.GetCollection<BsonDocument>(name).Indexes.CreateOneAsync(new CreateIndexModel<BsonDocument>(keys, indexOptions));
            }
        }
    }

    /// <summary>The stored documents a filter finds, as MongoDB's JSON, one line each.</summary>
    public async Task<IReadOnlyList<string>> FindAsync(string collection, string filterJson)
    {
        var documents = await _database.GetCollection<BsonDocument>(collection).Find(BsonDocument.Parse(filterJson)).ToListAsync();
        return documents.Select(x => x.ToJson()).ToList();
    }
}

  > 1. Preload at startup
      lead: id _id (String, generated), keys (email), fields email, full_name, score, captured_on
  > 2. Create through the preloaded service
      created lead-m701@example.com
      caught ArxValidationException: ARX4004 DataTypeMismatch: Attribute 'score' on 'lead' is a String, but the preloaded schema says 'score' holds int (Int32).
  > 3. Strict
      caught ArxValidationException: ARX1018 NotPreloaded: Column 'scroe' of 'lead' isn't in the preloaded schema, and the service is Strict.