Marten Single Stream Projection

Follow this guide to create a Single Stream Projection in Marten. This projection creates a single document for a single event stream (aggregate instance).

1. Define the Projection Class

   • Create a class in src/BookStore.ApiService/Projections/
   • Naming: {Resource}Projection (e.g., AuthorDetailsProjection)
   • Base Class: SingleStreamProjection<T> matches the standard pattern for explicit single stream aggregation.
   • Template: templates/Projection.cs

2. Configure in Marten

   • Open src/BookStore.ApiService/Infrastructure/Extensions/MartenConfigurationExtensions.cs
   • Register the projection in RegisterProjections:

     options.Projections.Add<AuthorDetailsProjection>(ProjectionLifecycle.Async);
     

   • Note: Async is recommended for performance. Inline handles consistency but impacts write performance.

3. Indexing (Optional)

   • In ConfigureIndexes:

     options.Schema.For<AuthorDetailsProjection>().Index(x => x.Name);
     

4. Querying

   • Query this projection by ID (matching the stream ID) or other fields.
   • Example: session.LoadAsync<AuthorDetailsProjection>(streamId)

Related Skills

• /marten__aggregate_scaffold: Create the events first.
• /marten__get_by_id: Create an endpoint to query this projection.
• /marten__list_query: Create list endpoints if the projection supports browsing.