Inject a service class into a projection

[ronikurnia1]

I think this is powerful if we can inject a service class (using DI) into a projection, something like this:

public class MyProjection : SingleStreamAggregation<MyReadModel>
{
    private readonly IAggregateRepository repository;
    public MyProjection (IAggregateRepository repository)
    {
        this.repository = repository;
    }
}

[jeremydmiller]

@ronikurnia1 You can use DI services in projections as is. Check the flavor of AddMarten that takes in a Func<IServiceProvider, StoreOptions> argument to add projections with service dependencies. You'd be completely responsible for any service lifecycle

[ronikurnia1]

@jeremydmiller thanks for the response.
I've tried the following code:

builder.Services.AddMarten(options =>
{
    options.Projections.Add<MyProjection>();
}

But Matren rejected it, asking for a public parameter-less constructor class

Did I miss something here?

[gfoidl]

Add an instance of the projection instead of defining it with the generic type.

E.g.

appBuilder.Services.AddMarten(serviceProvider =>
{
    StoreOptions options = new();

    // Configuration as usual

    MyProjection myProjection = new(serviceProvider.GetRequiredService<IMyServiceToUseInProjection>());
    options.Projections.Add(myProjection, ProjectionLifecycle.Async);

    return options;
});


public class MyProjection : SingleStreamProjection<MyView>
{
    public MyProjection(IMyServiceToUseInProjection foo)
    {
        // ...
    }
}