public void AddMember(Guid memberId)
{
if(_members.Contains(memberId)) throw new DomainException(string.Format("Already contains member with id {0}.", memberId));
var e = new MemberAddedToProject(memberId);
ApplyEvent(e);
}
private void OnMemberAdded(MemberAddedToProject e)
{
_members.Add(e.MemberId);
}