Useful feature for Delta<T> - Get previous and current values for changed properties

gistfile1.cs

public Dictionary<string, Tuple<object, object>> GetChanges(TEntityType original)
{
    if (original == null)
    {
        throw new ArgumentNullException("original");
    }

    if (!_entityType.IsAssignableFrom(original.GetType()))
    {
        throw new InvalidOperationException(string.Format("Entity mismatch exception between {0} and {1}", _entityType, original.GetType()));
    }

    PropertyAccessor<TEntityType>[] properties = GetChangedPropertyNames().Select(s => _propertiesThatExist[s]).ToArray();

    return properties.ToDictionary(
        property => property.Property.Name,
        property => new Tuple<object, object>(property.GetValue(this._entity), property.GetValue(original)));
}