使用 CQRS 和事件溯源的状态模式

Question

I am using CQRS with Event Sourcing and I am trying to use the state pattern with my aggregate root.

I currently have a product domain model with a couple methods called Create() and CreateSubscription like below.

public static void Create(string name){        
    When(new ProductCreatedEvent { Name = name});
}

public void CreateSubscription(string name){        
    if(_productState.CanCreateSubscription()){
        When(new SubscriptionCreatedEvent { Name = name});
    }        
}

Then I have the private methods that actually sets the values like below.

private void OnCreated(ProductCreatedEvent e){
     _name = e.Name;
}

private void OnSubscriptionCreated(SubscriptionCreatedEvent e){
     _subscriptions.Add(Subscription.Create(e.Name));
}

When I have used the state pattern before using DDD the logic was moved into the state class but because I am using event sourcing I need to call the When method which is in a base class which then invokes my private 'On' methods which actually sets the values.

I was wondering how to move that logic into my state class, otherwise at the moment my state class only has 'Can' methods on it and not the actual implementation code.

Answer 1

Can you not just pass things into _productState?

private void OnSomeEvent(SomeEvent e){
    _productState.Something(); // pass in e?
}

For example:

public void CreateSubscription(string name){        
    _productState.CreateSubscription(name); 
}

public class ProductState
{
    public void CreateSubscription(string name)
    {
        if (this.CanCreateSubscription())
        {
            _subscriptions.Add(Subscription.Create(name));
        }
    }
}

Or

public void OnSomeEventThatMeansYouCanCreateASubscription(string name)
{   
    _productState.EnableCreateSubscription(name);     
}

public void OnSomeEventThatNeedsToCheckTheState(string name)
{   
    if (_productState.CanCreateSubscription())     
        _subscriptions.Add(Subscription.Create(name));
}