Bootstrapping in .Net Applications

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The exact formula for bootstrapping .Net applications has changed quite a bit from early .Net Core to the latest WebApplication model in .Net 6.0 at the time this page was last updated. Regardless, the IServiceCollection abstraction for registering services in an IoC container has remained stable and everything in this page functions against that model.

As briefly shown in the getting started page, Marten comes with extension methods for the .Net Core standard IServiceCollection to quickly add Marten services to any .Net application that is bootstrapped by either the Generic IHostBuilder abstraction or the ASP.Net Core IWebHostBuilder or the .Net 6 WebApplication hosting models.

Jumping right into a basic ASP.NET Core application using the out of the box Web API template, you'd have a class called Startup that holds most of the configuration for your application including the IoC service registrations for your application in the Startup.ConfigureServices() method. To add Marten to your application, use the AddMarten() method as shown below:

public void ConfigureServices(IServiceCollection services)
{
    // This is the absolute, simplest way to integrate Marten into your
    // .Net Core application with Marten's default configuration
    services.AddMarten(options =>
    {
        // Establish the connection string to your Marten database
        options.Connection(Configuration.GetConnectionString("Marten"));

        // If we're running in development mode, let Marten just take care
        // of all necessary schema building and patching behind the scenes
        if (Environment.IsDevelopment())
        {
            options.AutoCreateSchemaObjects = AutoCreate.All;
        }
    });
}
// and other methods we don't care about right now...

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The AddMarten() method will add these service registrations to your application:

  1. IDocumentStore with a Singleton lifetime. The document store can be used to create sessions, query the configuration of Marten, generate schema migrations, and do bulk inserts.
  2. IDocumentSession with a Scoped lifetime for all read and write operations. By default, this is done with the IDocumentStore.OpenSession() method and the session created will have the identity map behavior
  3. IQuerySession with a Scoped lifetime for all read operations against the document store.

For more information, see:

At runtime, when your application needs to resolve IDocumentStore for the first time, Marten will:

  1. Resolve a StoreOptions object from the initial AddMarten() configuration
  2. Apply all registered IConfigureMarten services to alter that StoreOptions object
  3. Reads the IHostEnvironment for the application if it exists to try to determine the main application assembly and paths for generated code output
  4. Attaches any IInitialData services that were registered in the IoC container to the StoreOptions object
  5. Finally, Marten builds a new DocumentStore object using the now configured StoreOptions object

This model is comparable to the .Net IOptions model.

Register DocumentStore with AddMarten()

INFO

All the examples in this page are assuming the usage of the default IoC container Microsoft.Extensions.DependencyInjection, but Marten can be used with any IoC container or with no IoC container whatsoever.

First, if you are using Marten completely out of the box with no customizations (besides attributes on your documents), you can just supply a connection string to the underlying Postgresql database like this:

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {

        var connectionString = Configuration.GetConnectionString("postgres");

        // By only the connection string
        services.AddMarten(connectionString);
    }

    // And other methods we don't care about here...
}

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The second option is to supply a nested closure to configure Marten inline like so:

public class Startup
{
    public IConfiguration Configuration { get; }
    public IHostEnvironment Hosting { get; }

    public Startup(IConfiguration configuration, IHostEnvironment hosting)
    {
        Configuration = configuration;
        Hosting = hosting;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        var connectionString = Configuration.GetConnectionString("postgres");

        services.AddMarten(opts =>
        {
            opts.Connection(connectionString);

            // Use the more permissive schema auto create behavior
            // while in development
            if (Hosting.IsDevelopment())
            {
                opts.AutoCreateSchemaObjects = AutoCreate.All;
            }
        });
    }

    // And other methods we don't care about here...
}

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Lastly, if you prefer, you can pass a Marten StoreOptions object to AddMarten() like this example:

public class Startup
{
    public IConfiguration Configuration { get; }
    public IHostEnvironment Hosting { get; }

    public Startup(IConfiguration configuration, IHostEnvironment hosting)
    {
        Configuration = configuration;
        Hosting = hosting;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        var options = BuildStoreOptions();

        services.AddMarten(options);
    }

    private StoreOptions BuildStoreOptions()
    {
        var connectionString = Configuration.GetConnectionString("postgres");

        // Or lastly, build a StoreOptions object yourself
        var options = new StoreOptions();
        options.Connection(connectionString);

        // Use the more permissive schema auto create behavior
        // while in development
        if (Hosting.IsDevelopment())
        {
            options.AutoCreateSchemaObjects = AutoCreate.All;
        }

        return options;
    }

    // And other methods we don't care about here...
}

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The last option may be best for more complicated Marten configuration just to keep the configuration code cleaner as Startup classes can become convoluted.

Composite Configuration with ConfigureMarten()

The AddMarten() mechanism introduced in later versions of Marten v3 assumes that you are expressing all of the Marten configuration in one place and "know" what that configuration is upfront. Consider these possibilities where that isn't necessarily possible or desirable:

  1. You want to override Marten configuration in integration testing scenarios (I do this quite commonly)
  2. Many users have expressed the desire to keep parts of Marten configuration in potentially separate assemblies or subsystems in such a way that they could later break up the current service into smaller services

Fear not, Marten V5.0 introduced a new way to add or modify the Marten configuration from AddMarten(). Let's assume that we're building a system that has a subsystem related to users and want to segregate all the service registrations and Marten configuration related to users into a single place like this extension method:

public static IServiceCollection AddUserModule(this IServiceCollection services)
{
    // This applies additional configuration to the main Marten DocumentStore
    // that is configured elsewhere
    services.ConfigureMarten(opts =>
    {
        opts.RegisterDocumentType<User>();
    });

    // Other service registrations specific to the User submodule
    // within the bigger system

    return services;
}

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And next, let's put that into context with its usage inside your application's bootstrapping:

using var host = await Host.CreateDefaultBuilder()
    .ConfigureServices(services =>
    {
        // The initial Marten configuration
        services.AddMarten("some connection string");

        // Other core service registrations
        services.AddLogging();

        // Add the User module
        services.AddUserModule();
    }).StartAsync();

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The ConfigureMarten() method is the interesting part of the code samples above. That is registering a small service that implements the IConfigureMarten interface into the underlying IoC container:

/// <summary>
/// Mechanism to register additional Marten configuration that is applied after AddMarten()
/// configuration, but before DocumentStore is initialized
/// </summary>
public interface IConfigureMarten
{
    void Configure(IServiceProvider services, StoreOptions options);
}

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You could alternatively implement a custom IConfigureMarten class like so:

internal class UserMartenConfiguration: IConfigureMarten
{
    public void Configure(IServiceProvider services, StoreOptions options)
    {
        options.RegisterDocumentType<User>();
        // and any other additional Marten configuration
    }
}

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and registering it in your IoC container something like this:

public static IServiceCollection AddUserModule2(this IServiceCollection services)
{
    // This applies additional configuration to the main Marten DocumentStore
    // that is configured elsewhere
    services.AddSingleton<IConfigureMarten, UserMartenConfiguration>();

    // Other service registrations specific to the User submodule
    // within the bigger system

    return services;
}

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Using Lightweight Sessions

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Most usages of Marten should default to the lightweight sessions for better performance

The default registration for IDocumentSession added by AddMarten() is a session with identity map mechanics. That might be unnecessary overhead in most cases where the sessions are short-lived, but we keep this behavior for backward compatibility with early Marten and RavenDb behavior before that. To opt into using lightweight sessions without the identity map behavior, use this syntax:

public class Startup
{
    public Startup(IConfiguration configuration, IHostEnvironment hosting)
    {
        Configuration = configuration;
        Hosting = hosting;
    }

    public IConfiguration Configuration { get; }
    public IHostEnvironment Hosting { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        var connectionString = Configuration.GetConnectionString("postgres");

        services.AddMarten(opts =>
        {
            opts.Connection(connectionString);
        })

        // Chained helper to replace the built in
        // session factory behavior
        .UseLightweightSessions();
    }

    // And other methods we don't care about here...
}

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Customizing Session Creation Globally

By default, Marten will create a document session with the basic identity map enabled and a ReadCommitted transaction isolation level. If you want to use a different configuration for sessions globally in your application, you can use a custom implementation of the ISessionFactory class as shown in this example:

public class CustomSessionFactory: ISessionFactory
{
    private readonly IDocumentStore _store;

    // This is important! You will need to use the
    // IDocumentStore to open sessions
    public CustomSessionFactory(IDocumentStore store)
    {
        _store = store;
    }

    public IQuerySession QuerySession()
    {
        return _store.QuerySession();
    }

    public IDocumentSession OpenSession()
    {
        // Opting for the "lightweight" session
        // option with no identity map tracking
        // and choosing to use Serializable transactions
        // just to be different
        return _store.LightweightSession(IsolationLevel.Serializable);
    }
}

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To register the custom session factory, use the BuildSessionsWith() method as shown in this example:

public class Startup
{
    public Startup(IConfiguration configuration, IHostEnvironment hosting)
    {
        Configuration = configuration;
        Hosting = hosting;
    }

    public IConfiguration Configuration { get; }
    public IHostEnvironment Hosting { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        var connectionString = Configuration.GetConnectionString("postgres");

        services.AddMarten(opts =>
            {
                opts.Connection(connectionString);

                // Use the more permissive schema auto create behavior
                // while in development
                if (Hosting.IsDevelopment())
                {
                    opts.AutoCreateSchemaObjects = AutoCreate.All;
                }
            })

            // Chained helper to replace the built in
            // session factory behavior
            .BuildSessionsWith<CustomSessionFactory>();
    }

    // And other methods we don't care about here...
}

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The session factories can also be used to build out and attach custom IDocumentSessionListener objects or replace the logging as we'll see in the next section.

See diagnostics and instrumentation for more information.

Customizing Session Creation by Scope

From a recent user request to Marten, what if you want to log the database statement activity in Marten with some kind of correlation to the active HTTP request or service bus message or some other logical session identification in your application? That's now possible by using a custom ISessionFactory.

Taking the example of an ASP.NET Core application, let's say that you have a small service scoped to an HTTP request that tracks a correlation identifier for the request like this:

public interface ISession
{
    Guid CorrelationId { get; set; }
}

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And a custom Marten session logger to add the correlation identifier to the log output like this:

public class CorrelatedMartenLogger: IMartenSessionLogger
{
    private readonly ILogger<IDocumentSession> _logger;
    private readonly ISession _session;

    public CorrelatedMartenLogger(ILogger<IDocumentSession> logger, ISession session)
    {
        _logger = logger;
        _session = session;
    }

    public void LogSuccess(NpgsqlCommand command)
    {
        // Do some kind of logging using the correlation id of the ISession
    }

    public void LogFailure(NpgsqlCommand command, Exception ex)
    {
        // Do some kind of logging using the correlation id of the ISession
    }

    public void RecordSavedChanges(IDocumentSession session, IChangeSet commit)
    {
        // Do some kind of logging using the correlation id of the ISession
    }

    public void OnBeforeExecute(NpgsqlCommand command)
    {

    }
}

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Now, let's move on to building out a custom session factory that will attach our correlated marten logger to sessions being resolved from the IoC container:

public class ScopedSessionFactory: ISessionFactory
{
    private readonly IDocumentStore _store;
    private readonly ILogger<IDocumentSession> _logger;
    private readonly ISession _session;

    // This is important! You will need to use the
    // IDocumentStore to open sessions
    public ScopedSessionFactory(IDocumentStore store, ILogger<IDocumentSession> logger, ISession session)
    {
        _store = store;
        _logger = logger;
        _session = session;
    }

    public IQuerySession QuerySession()
    {
        return _store.QuerySession();
    }

    public IDocumentSession OpenSession()
    {
        var session = _store.LightweightSession();

        // Replace the Marten session logger with our new
        // correlated marten logger
        session.Logger = new CorrelatedMartenLogger(_logger, _session);

        return session;
    }
}

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Lastly, let's register our new session factory, but this time we need to take care to register the session factory as Scoped in the underlying container so we're using the correct ISession at runtime:

public class Startup
{
    public IConfiguration Configuration { get; }
    public IHostEnvironment Hosting { get; }

    public Startup(IConfiguration configuration, IHostEnvironment hosting)
    {
        Configuration = configuration;
        Hosting = hosting;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        var connectionString = Configuration.GetConnectionString("postgres");

        services.AddMarten(opts =>
        {
            opts.Connection(connectionString);

            // Use the more permissive schema auto create behavior
            // while in development
            if (Hosting.IsDevelopment())
            {
                opts.AutoCreateSchemaObjects = AutoCreate.All;
            }
        })
        // Chained helper to replace the CustomSessionFactory
        .BuildSessionsWith<ScopedSessionFactory>(ServiceLifetime.Scoped);
    }

    // And other methods we don't care about here...
}

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This correlation tracking might be better with structural logging with something like Serilog, but we'll leave that to users.

Eager Initialization of the DocumentStore

Lastly, if desirable, you can force Marten to initialize the applications document store as part of bootstrapping instead of waiting for it to be initialized on the first usage with this syntax:

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {

        var connectionString = Configuration.GetConnectionString("postgres");

        // By only the connection string
        services.AddMarten(connectionString)

            // Spin up the DocumentStore right this second!
            .InitializeStore();
    }

    // And other methods we don't care about here...
}

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Working with Multiple Marten Databases

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This feature is not meant for multi-tenancy with separate databases. This is specifically meant for use cases where a single system needs to work with two or more semantically different Marten databases.

TIP

The database management tools in Marten.CommandLine are able to work with the separately registered document stores along with the default store from AddMarten().

Marten V5.0 introduces a new feature to register additional Marten databases into a .Net system. AddMarten() continues to work as it has, but we can now register and resolve additional store services. To utilize the type system and your application's underlying IoC container, the first step is to create a custom marker interface for your separate document store like this one below targeting a separate "invoicing" database:

// These marker interfaces *must* be public
public interface IInvoicingStore : IDocumentStore
{

}

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A couple notes on the interface:

  1. The custom interface has to be public and implement the IDocumentStore interface
  2. Marten is quietly building a dynamic type for your additional store interface internally

And now to bootstrap that separate store in our system:

using var host = Host.CreateDefaultBuilder()
    .ConfigureServices(services =>
    {
        // You can still use AddMarten() for the main document store
        // of this application
        services.AddMarten("some connection string");

        services.AddMartenStore<IInvoicingStore>(opts =>
            {
                // All the normal options are available here
                opts.Connection("different connection string");

                // more configuration
            })
            // Optionally apply all database schema
            // changes on startup
            .ApplyAllDatabaseChangesOnStartup()

            // Run the async daemon for this database
            .AddAsyncDaemon(DaemonMode.HotCold)

            // Use IInitialData
            .InitializeWith(new DefaultDataSet())

            // Use the V5 optimized artifact workflow
            // with the separate store as well
            .OptimizeArtifactWorkflow();
    }).StartAsync();

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At runtime we can inject an instance of our new IInvoicingStore and work with it like any other Marten IDocumentStore as shown below in an internal InvoicingService:

public class InvoicingService
{
    private readonly IInvoicingStore _store;

    // IInvoicingStore can be injected like any other
    // service in your IoC container
    public InvoicingService(IInvoicingStore store)
    {
        _store = store;
    }

    public async Task DoSomethingWithInvoices()
    {
        // Important to dispose the session when you're done
        // with it
        await using var session = _store.LightweightSession();

        // do stuff with the session you just opened
    }
}

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