Enforcing parent-child relationship in C# and .Net

Question

Let\'s take the following two classes:

public class CollectionOfChildren
{
    public Child this[int index] { get; }
    public void Add(Child c);
}

public          


        

Answer 1

I was also looking into it recently, and thought about really enforcing this relationship as error proof as possible. Additionally, I tried to keep it as general and type safe as possible. It may be just overengineered, but still I would like to share it.

public class ChildCollection : IEnumerable 
    where TChild : ChildCollection.Child
{
    private readonly List childCollection = new List();

    private void Add(TChild child) => this.childCollection.Add(child);

    public IEnumerator GetEnumerator() => this.childCollection.GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

    public abstract class Child
    {
        private readonly ChildCollection childCollection;

        protected Child(ChildCollection childCollection)
        {
            this.childCollection = childCollection;
            childCollection.Add((TChild)this);
        }
    }
}

Here comes the Example:

public class Parent
{
    public ChildCollection ChildCollection { get; }
    public Parent()
    {
        ChildCollection = new ChildCollection();
    }
}

public class Child : ChildCollection.Child
{
   public Child(ChildCollection childCollection) : base(childCollection)
   {
   }
}

And adding a child to the parent would look like:

var parent = new Parent();
var child1 = new Child(parent.ChildCollection);

The final implementation also has Ids for the children and allows removing of children. But the latter destroys the strong enforcement of the parent child relationship.