对象组合的实现模式

Question

我在映射这些类时遇到了困难：

• 阶
• 托盘
• Box

它们结合在一起形成了一个构图关系，详见这篇维基百科文章。

类Order的实例有几个托盘对象，其中有几个Box对象。

这就是我现在拥有的：

class Order
{
    public Order(){}
    private List<Pallet> _pallets = new List<Pallet>;
    public Pallet Add_pallet()
    {
        Pallet new_pallet = new Pallet(this);
        this._pallets.Add(new_pallet);
        return new_pallet;
    }
    //...other properties and methods...
}

class Pallet
{
    private Order _parent_order;
    private List<Box> _boxes = new List<Box>;
    public Pallet(Order parent_order)
    {
        _parent_order = parent_order;
    }
    public Box Add_Box()
    {
        Box new_box = new Box(this);
        this._boxes.Add(new_box);
        return new_box;
    }
    //...other properties and methods...
}

class Box
{
    private Pallet _parent_pallet;
    public Box(Pallet parent_pallet){}
    //...other properties and methods...
}

所有盒必须属于托盘，而托盘必须属于Order。

如何正确地实现这一点以避免这种情况：

static class Program
{
    static void Main()
    {
        Order myOrder = new Order();
        Pallet myPallet = new Pallet(myOrder);
        //Now I have a Pallet that belongs to an Order,
        //but the Order object is not aware of it
    }
}

我应该使用嵌套类还是缺少更有用的东西？

Answer 1

我会这样做：

public class Order
{
    private List<Pallet> _pallets = new List<Pallet>;
    internal void Add_pallet(Pallet pallet)
    {
        if (!this._pallets.Contains(pallet))
            this._pallets.Add(pallet);
    }
    //...other properties and methods...
}

public class Pallet
{
    private Order _parent_order;
    private List<Box> _boxes = new List<Box>;
    public Pallet(Order parent_order)
    {
        if (parent_order = null)
            throw ArgumentNilException("parent_order must not be null");
        _parent_order = parent_order;
        _parent_order.Add_pallet(this);
    }
    //...other properties and methods...
}

麻生太郎。