Domain Driven Design - Parent child relation pattern - Specification pattern

Question

I was wondering which of the following is considered to be a best practice when dealing with parent child relationships.

1) The following example seems to be a commo

Answer 1

Since I've just encountered the same design desissions and question still not marked as answered I'll post my vision on solution of this problem - maybe it'll help anyone. This solution actually perfectly viable for use with NHibernate.

public class Parent
{
    private readonly ISet _children = new HashedSet ();
    public virtual IEnumerable Children { get { return new ImmutableSet (this._children); }  }


    protected internal virtual void AddChild (Child child)
    {
        this._children.Add(child);
    }
}


public class Child
{
    public virtual Parent Parent { get; protected set; }


    protected Child()
    {
    }


    public static Create (Parent parent)
    {
        if (parent == null)
            throw new ArgumentNullException ("parent");

        var child = new Child
        {
            Parent = parent
        };

        child.Parent.AddChild (child);

        return child;
    }
}

That's differs from your #2 option in a way that creation of the child object (and invalidating it's initial values) are gathered withing child object itself and not in parent object as you suggested in #2.

Tho one thing I'm not sure if it's considered bad design or not if we create child objects with personal factory method (Child.Create).

I hope someone with more experience in using DDD could comment on that.