marten__multi_stream_projection

Follow this guide to create a Multi-Stream Projection (View Projection) in Marten. This allows you to aggregate data across many different streams into a single document (or multiple documents based on grouping).

1. Define the Projection Class

   • Create a class in src/BookStore.ApiService/Projections/
   • Naming: {Summary}Projection (e.g., AuthorDashboardProjection or MonthlySalesProjection)
   • Base Class: MultiStreamProjection<T, TId>
   • Template: templates/Projection.cs

2. Configure in Marten

   • Open src/BookStore.ApiService/Infrastructure/Extensions/MartenConfigurationExtensions.cs
   • Register:
     csharpCopy

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

3. Indexing

   • Add indexes in ConfigureIndexes if you need to query by fields other than Id.

Related Skills

• /marten__single_stream_projection: If you only need data from one stream.
• /marten__event_projection: If you need 1:1 transformation without aggregation.