Lazy-loaded NHibernate properties in Equals and GetHashCode

Question

How can the following problem be dealt with?

We\'re using lazy loaded NHibernate properties and whenever we\'re calling Equals() or GetHashCode()<

Answer 1

If you are using identity equality, you should be able to access the key without triggering a load:

public virtual bool Equals(ClassB other)
{
    if (ReferenceEquals(null, other))
    {
        return false;
    }
    if (ReferenceEquals(this, other))
    {
        return true;
    }
    // needs to check for null Id
    return Equals(other.ClassC.Id, ClassC.Id) && Equals(other.ClassD.Id, ClassD.Id);
}

You can handle comparisons between objects before and after persisting by caching the hash code when it was transient. This leaves a small gap in the Equals contract in that a comparison between an existing object that was transient will not generate the same hash code as a newly-retrieved version of the same object.

public abstract class Entity
{
    private int? _cachedHashCode;

    public virtual int EntityId { get; private set; }

    public virtual bool IsTransient { get { return EntityId == 0; } }

    public override bool Equals(object obj)
    {
        if (obj == null)
        {
            return false;
        }
        var other = obj as Entity;
        return Equals(other);
    }

    public virtual bool Equals(Entity other)
    {
        if (other == null)
        {
            return false;
        }
        if (IsTransient ^ other.IsTransient)
        {
            return false;
        }
        if (IsTransient && other.IsTransient)
        {
            return ReferenceEquals(this, other);
        }
        return EntityId.Equals(other.EntityId);
    }

    public override int GetHashCode()
    {
        if (!_cachedHashCode.HasValue)
        {
            _cachedHashCode = IsTransient ? base.GetHashCode() : EntityId.GetHashCode();
        }
        return _cachedHashCode.Value;
    }
}