ascending/descending in LINQ – can one change the order via parameter?

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You can easily create your own extension method on IEnumerable or IQueryable:

public static IOrderedEnumerable<TSource> OrderByWithDirection<TSource,TKey>
    (this IEnumerable<TSource> source,
     Func<TSource, TKey> keySelector,
     bool descending)
{
    return descending ? source.OrderByDescending(keySelector)
                      : source.OrderBy(keySelector);
}

public static IOrderedQueryable<TSource> OrderByWithDirection<TSource,TKey>
    (this IQueryable<TSource> source,
     Expression<Func<TSource, TKey>> keySelector,
     bool descending)
{
    return descending ? source.OrderByDescending(keySelector)
                      : source.OrderBy(keySelector);
}

Yes, you lose the ability to use a query expression here – but frankly I don’t think you’re actually benefiting from a query expression anyway in this case. Query expressions are great for complex things, but if you’re only doing a single operation it’s simpler to just put that one operation:

var query = dataList.OrderByWithDirection(x => x.Property, direction);

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