Transient triggers should share state between its life-cycle implementations

Currently transient triggers do not share state between the different lifecycles, e.g;

class MyTrigger : IBeforeSaveTrigger<object>, IAfterSaveTrigger<object> { 
    int _counter;
    
    public Task BeforeSave(ITriggerContext<object> context, CancellationToken _) {
        _counter += 1;
        return Task.CompletedTask;
    }
    
    public Task AfterSave(ITriggerContext<object> context, CancellationToken _) {
        Console.WriteLine($"Counter: {_counter}");
        return Task.CompletedTask;
    }
}

Will always print 0 when registered as a transient trigger since state is not shared between the 2 lifecycles. If we were to register the trigger as a Scoped trigger then the counter may be > 1 if there are multiple entities within the changeset.

It makes sense to have transient triggers still share the same state so that a Trigger is only transient per unique Entity/Trigger, not per unique Entity/Lifecyle as its currently.

[koenbeuk]

@DavidErben Yes my bad, the default Lifetime for AddTrigger is Transient, not Scoped. I’ve updated my reply above. Thanks for pointing that out!

[koenbeuk]

I have a hypothetical fix for this issue implemented in #115

This exposes a new EntityBag property on the TriggerContext which in turn can be used to associate additional items with the entity for the duration of the Trigger session.

A sample usage is given here: https://github.com/koenbeuk/EntityFrameworkCore.Triggered/blob/trigger-entity-state-management/test/EntityFrameworkCore.Triggered.IntegrationTests/EntityBags/EntityBagsTestScenario.cs

Feedback is welcome