Dynamic SQL-like Linq OrderBy Extension

So, it's been a while, but I thought I take moment and do my annual blog post ;).

I've been playing around with ASP.NET MVC and the Linq stuff for NHibernate recently. I was in need of an OrderBy extension method that could take a SQL-Like OrderBy string and sort a IQueryable<> or IEnumerable<> collection. I wrote up an implementation that worked, but I just wasn't satisfied with its internals (quite a bit of reflection to get the correct type to construct a LambdaExpression, etc)

At any rate, I couldn't leave well enough alone, and, after a bit of Googling, I ran across this StackOverflow answer about Dynamic LINQ OrderBy. The extension method wasn't exactly what I was looking for, but that ApplyOrder method is slick, and solved the portion of my implementation that was bothering me.

So, I though I would post up my version in case anybody finds it useful. It handles the following inputs:

list.OrderBy("SomeProperty");
list.OrderBy("SomeProperty DESC");
list.OrderBy("SomeProperty DESC, SomeOtherProperty");
list.OrderBy("SomeSubObject.SomeProperty ASC, SomeOtherProperty DESC");

Dynamic SQL-like Linq OrderBy Extension

    public static class OrderByHelper
    {
        public static IEnumerable<T> OrderBy<T>(this IEnumerable<T> enumerable, string orderBy)
        {
            return enumerable.AsQueryable().OrderBy(orderBy).AsEnumerable();
        }

        public static IQueryable<T> OrderBy<T>(this IQueryable<T> collection, string orderBy)
        {
            foreach(OrderByInfo orderByInfo in ParseOrderBy(orderBy))
                collection = ApplyOrderBy<T>(collection, orderByInfo);

            return collection;
        }

        private static IQueryable<T> ApplyOrderBy<T>(IQueryable<T> collection, OrderByInfo orderByInfo)
        {
            string[] props = orderByInfo.PropertyName.Split('.');
            Type type = typeof(T);

            ParameterExpression arg = Expression.Parameter(type, "x");
            Expression expr = arg;
            foreach (string prop in props)
            {
                // use reflection (not ComponentModel) to mirror LINQ
                PropertyInfo pi = type.GetProperty(prop);
                expr = Expression.Property(expr, pi);
                type = pi.PropertyType;
            }
            Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
            LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
            string methodName = String.Empty;

            if (!orderByInfo.Initial && collection is IOrderedQueryable<T>)
            {
                if (orderByInfo.Direction == SortDirection.Ascending)
                    methodName = "ThenBy";
                else
                    methodName = "ThenByDescending";
            }
            else
            {
                if (orderByInfo.Direction == SortDirection.Ascending)
                     methodName = "OrderBy";
                else
                     methodName = "OrderByDescending";
            }

            //TODO: apply caching to the generic methodsinfos?
            return (IOrderedQueryable<T>)typeof(Queryable).GetMethods().Single(
                method => method.Name == methodName
                        && method.IsGenericMethodDefinition
                        && method.GetGenericArguments().Length == 2
                        && method.GetParameters().Length == 2)
                .MakeGenericMethod(typeof(T), type)
                .Invoke(null, new object[] { collection, lambda });

        }

        private static IEnumerable<OrderByInfo> ParseOrderBy(string orderBy)
        {
            if (String.IsNullOrEmpty(orderBy))
                yield break;

            string[] items = orderBy.Split(',');
            bool initial = true;
            foreach(string item in items)
            {
                string[] pair = item.Trim().Split(' ');

                if (pair.Length > 2)
                    throw new ArgumentException(String.Format("Invalid OrderBy string '{0}'. Order By Format: Property, Property2 ASC, Property2 DESC",item));

                string prop = pair[0].Trim();

                if(String.IsNullOrEmpty(prop))
                    throw new ArgumentException("Invalid Property. Order By Format: Property, Property2 ASC, Property2 DESC");
                
                SortDirection dir = SortDirection.Ascending;
                
                if (pair.Length == 2)
                    dir = ("desc".Equals(pair[1].Trim(), StringComparison.OrdinalIgnoreCase) ? SortDirection.Descending : SortDirection.Ascending);

                yield return new OrderByInfo() { PropertyName = prop, Direction = dir, Initial = initial };

                initial = false;
            }

        }

        private class OrderByInfo
        {
            public string PropertyName { get; set; }
            public SortDirection Direction { get; set; }
            public bool Initial { get; set; }
        }

        private enum SortDirection
        {
            Ascending = 0,
            Descending = 1
        }
    }

Anyway, hope someone finds it useful. And if you see any areas that could use some TLC please let me know A