How to manually set the mt_events.id property

[mumby0168]

Pasting from discussion here hoping for an answer 😄

#3602

Hi, I have a scenario where we get an event from an external system, this event is mapped and written to a marten event store for auditing.

I have enabled the unique key index on the ID column and would like to manually set the ID on my event records. I think from the docs it just asks to set an property such as Guid Id however, this does not appear to work. Demo app below. Any support appreciated.

https://github.com/mumby0168/marten-id-demo

for ease of viewing here is the code snippet:

using System.Text.Json;
using System.Text.Json.Serialization;
using JasperFx.Core;
using Marten;
using Marten.Events;
using Marten.Services;
using MartenIdDemo.Events;
using Weasel.Core;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddMarten(
    martenOptions =>
    {
        var connectionString = builder.Configuration.GetConnectionString("DefaultConnection")
                               ?? throw new InvalidOperationException("Please provide a connection string to Postgres via ConnectionStrings:DefaultConnection");

        martenOptions.Connection(connectionString);
        martenOptions.AutoCreateSchemaObjects = AutoCreate.CreateOrUpdate;

        martenOptions.Events.EnableUniqueIndexOnEventId = true;
        martenOptions.Events.StreamIdentity = StreamIdentity.AsString;

        martenOptions.OpenTelemetry.TrackEventCounters();
        martenOptions.OpenTelemetry.TrackConnections = TrackLevel.Normal;

        martenOptions.UseSystemTextJsonForSerialization(
            new JsonSerializerOptions
            {
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
                PropertyNameCaseInsensitive = true,
                Converters = { new JsonStringEnumConverter() }
            });
    });

var app = builder.Build();

var docStore = app.Services.GetRequiredService<IDocumentStore>();
await docStore.Storage.ApplyAllConfiguredChangesToDatabaseAsync();

app.MapGet("/", async (IDocumentStore documentStore) =>
{
    var id = Guid.NewGuid();

    var evt = new UserEvents.SignedUp(id, Guid.NewGuid().ToString());

    await using (var session = documentStore.LightweightSession())
    {
        session.Events.Append(evt.UserId, evt);
        await session.SaveChangesAsync();
    }
    
    await using (var session = documentStore.LightweightSession())
    {
        var returnedEvt = await session
            .Events
            .QueryAllRawEvents()
            .Where(x => x.Id == id)
            .ToListAsync();

        return Results.Ok(returnedEvt);

    }
});

app.Run();

[jeremydmiller]

@mumby0168 Next time could you use either discussions or better yet, Discord for questions? Here: https://discord.gg/cFy5Xctb

When you all Append() or StartStream() it returns a StreamAction object that does have the event objects you just put in wrapped as IEvent<T>. You could set the IEvent.Id off of that. Not exactly something that really comes up, but your use case makes sense to me

[mumby0168]

Thanks @jeremydmiller I just created this small extension method and it's working as I'd hoped :)

public static class EventStoreExtensions
    {
        public static StreamAction AppendWithId<T>(this IEventStore eventStore, string streamId, T evt, Func<T, Guid> idFunc) where T : class
        {
            var stream = eventStore.Append(streamId, evt);
            stream.Events.Single().Id = idFunc(evt);
            return stream;
        }
    }

how do you feel about either this or something similar been contributed to the library?