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copied!<p>Use separate entity to store relationships between objects. Like this:</p> <pre><code>[TestFixture] public class Tester { [Test] public void SetY() { var refs = new References(); var x = new X(refs); var y = new Y(refs); x.Y = y; Assert.AreSame(x.Y, y); Assert.AreSame(y.X, x); } [Test] public void SetYToNull() { var refs = new References(); var x = new X(refs); var y = new Y(refs); x.Y = y; y.X = null; Assert.IsNull(x.Y); Assert.IsNull(y.X); } } public class References { private IDictionary<X, Y> refs = new Dictionary<X, Y>(); public bool Contains(X x, Y y) { if (!refs.ContainsKey(x)) return false; if (refs[x] != y) return false; return true; } public void Delete(X x) { refs.Remove(x); } public void Add(X x, Y y) { refs.Add(x, y); } public Y Get(X x) { return refs.ContainsKey(x) ? refs[x] : null; } public X Get(Y y) { var pairs = refs.Where(r => r.Value == y); return pairs.Any() ? pairs.FirstOrDefault().Key : null; } public void Delete(Y y) { X x = Get(y); if (x != null) { Delete(x); } } } public class X { private readonly References refs; public X(References refs) { this.refs = refs; } public Y Y { get { return refs.Get(this); } set { if (value == null) { refs.Delete(this); } else { if (!refs.Contains(this, value)) { refs.Add(this, value); } } } } } public class Y { private References refs; public Y(References refs) { this.refs = refs; } public X X { get { return refs.Get(this); } set { if (value == null) { refs.Delete(this); } else { if (!refs.Contains(value, this)) { refs.Add(value, this); } } } } } </code></pre>

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