如何交叉引用类中的对象

Question

我有一个Person类和两个名为Parent和Child的继承类.父母可以有n个孩子,孩子可以有n个父母.

OOD在父和子之间创建引用的最佳方法是什么.

我应该在引用连接的父/子的每个类中创建一个List,还是有更好的方法？

Answer 1

好问题.纯粹的多对多关系实际上非常罕见,它通常有助于引入一个中间对象来模拟关系本身.如果(当!)用例出现需要捕获关于关系的属性(例如,子/父关系是自然的,代理的,收养的等),这将是非常宝贵的.

因此,除了您已经识别的Person,Parent和Child实体之外,让我们引入一个名为ParentChildRelationship的对象.ParentChildRelationship的实例将只引用一个Parent和One Child,Parent和Child类都将包含这些实体的集合.

然后,最好确定使用这些实体的用例,并添加适当的辅助方法来维护对象间引用.在下面的示例中,我刚刚选择将公共AddChild方法添加到父级.

public abstract class Person
{
}

public class Parent : Person
{
    private HashSet<ParentChildRelationship> _children = 
        new HashSet<ParentChildRelationship>();

    public virtual IEnumerable<ParentChildRelationship> Children
    {
        get { return this._children; }
    }

    public virtual void AddChild(Child child, RelationshipKind relationshipKind)
    {
        var relationship = new ParentChildRelationship()
        {
            Parent = this,
            Child = child,
            RelationshipKind = relationshipKind
        };

        this._children.Add(relationship);
        child.AddParent(relationship);
    }
}

public class Child : Person
{
    private HashSet<ParentChildRelationship> _parents = 
        new HashSet<ParentChildRelationship>();

    public virtual IEnumerable<ParentChildRelationship> Parents
    {
        get { return this._parents; }
    }

    internal virtual void AddParent(ParentChildRelationship relationship)
    {
        this._parents.Add(relationship);
    }
}

public class ParentChildRelationship
{
    public virtual Parent Parent { get; protected internal set; }

    public virtual Child Child { get; protected internal set; }

    public virtual RelationshipKind RelationshipKind { get; set; }
}

public enum RelationshipKind
{
    Unknown,
    Natural,
    Adoptive,
    Surrogate,
    StepParent
}