Add metadata to events

[peteglassey]

I cant seem to find it in the documentation, but how do we add metadata to our events that are going to eventstoredb? Eg i want to decorate each aggregate's event metadata with some additional information like version, content-type, scope (internal construct).

I thought it would be on the Apply() method on the Aggregate base class, but isnt.

In our aggregates we have command handling methods, that create the event and call Apply(), so i thought there might be an overload, but i cant find it.

I see there is a way to append metadata when publishing an event to a publisher (eg an 'integration' event etc), but nothing i can find when appending to aggregate's stream.

What did i miss?

[alexeyzimarev]

It's supported, but it's pretty weak in terms of the API. AggregateStore's constructor accepts a function, which allows you to add metadata, or do something else with the event that's going to be persisted. You would need to inspect the proposed StreamEvent and understand what you want to add in the meta. If you only want to add something generic like a timestamp or diagnostic data, then it will work just fine.

    public AggregateStore(
        IEventReader                    reader,
        IEventWriter                    writer,
        Func<StreamEvent, StreamEvent>? amendEvent      = null,
        AggregateFactoryRegistry?       factoryRegistry = null
    )

[alexeyzimarev]

An interface is not in any way better compared to named delegate, I generally avoid interfaces with one function in it, especially when it's called a Provider :) You can register functions just as you register other dependencies. I'd say it should be nullable, so if there's nothing provided there will be no call.

[peteglassey]

Alexey - are you intending to add this feature any time soon?

[alexeyzimarev]

It's already there #285

[peteglassey]

Thanks heaps

[alexeyzimarev]

It has never made to MyGet because of the failing tests in the pipeline (they actually pass but the container fails to report its health). I will hopefully fix it soon enough.