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Non Anemic Super Simple Event Sourced
public class Customer : AggregateRoot {
private string _name;
public Customer(Id customerId, string name)
Id = customerId;
Name = name;
ApplyEvent(new CustomerCreated(Id, Name)); //Again, passing already modified values;
public string Name {
get {
return _name;
private set {
if (string.IsNullOrEmpty(value))
throw new ArgumentNullException("Name is required"); //Single place where Name gets validated
_name = value;
public void ChangeName(string newName) {
this.Name = newName;
ApplyEvent(new CustomerNameChanged(this.Id, Name)); //PASSING THE MODIFIED NAME NOT THE PARAMETER
public void When(CustomerNameChanged @event){
this._name = @event.Name; //The event handler only modifies the internal state by passing the Setter that contains the validation
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yreynhout commented Jan 28, 2014

This is wrong! You should only change state in the When. Your validating property sounds like feature envy.

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