An extension method to filter a linq query with the field as a string

public static class EntityFrameworkExtensions
    {
        public static IOrderedQueryable OrderBy(this IQueryable query, string propertyName)
        {
            var entityType = typeof(TSource);

            //Create x=>x.PropName
            var propertyInfo = entityType.GetProperty(propertyName);
            ParameterExpression arg = Expression.Parameter(entityType, "x");
            MemberExpression property = Expression.Property(arg, propertyName);
            var selector = Expression.Lambda(property, new ParameterExpression[] { arg });

            //Get System.Linq.Queryable.OrderBy() method.
            var enumarableType = typeof(System.Linq.Queryable);
            var method = enumarableType.GetMethods()
                 .Where(m => m.Name == "OrderBy" && m.IsGenericMethodDefinition)
                 .Where(m =>
                 {
                     var parameters = m.GetParameters().ToList();
                     return parameters.Count == 2;
                 }).Single();

            //The linq's OrderBy<TSource, TKey> has two generic types, which provided here
            MethodInfo genericMethod = method.MakeGenericMethod(entityType, propertyInfo.PropertyType);

            // Call query.OrderBy(selector), with query and selector: x=> x.PropName
            // Note that we pass the selector as Expression to the method and we don't compile it.
            // By doing so EF can extract "order by" columns and generate SQL for it
            var newQuery = (IOrderedQueryable)genericMethod.Invoke(genericMethod, new object[] { query, selector });
            return newQuery;
        }

        public static IOrderedQueryable OrderByDescending(this IQueryable query, string propertyName)
        {
            var entityType = typeof(TSource);

            //Create x=>x.PropName
            var propertyInfo = entityType.GetProperty(propertyName);
            ParameterExpression arg = Expression.Parameter(entityType, "x");
            MemberExpression property = Expression.Property(arg, propertyName);
            var selector = Expression.Lambda(property, new ParameterExpression[] { arg });

            //Get System.Linq.Queryable.OrderBy() method.
            var enumarableType = typeof(System.Linq.Queryable);
            var method = enumarableType.GetMethods()
                 .Where(m => m.Name == "OrderByDescending" && m.IsGenericMethodDefinition)
                 .Where(m =>
                 {
                     var parameters = m.GetParameters().ToList();
                     return parameters.Count == 2;
                 }).Single();

            //The linq's OrderByDescending<TSource, TKey> has two generic types, which provided here
            MethodInfo genericMethod = method.MakeGenericMethod(entityType, propertyInfo.PropertyType);

            // Call query.OrderByDescending(selector), with query and selector: x=> x.PropName
            // Note that we pass the selector as Expression to the method and we don't compile it.
            // By doing so EF can extract "order by" columns and generate SQL for it
            var newQuery = (IOrderedQueryable)genericMethod.Invoke(genericMethod, new object[] { query, selector });
            return newQuery;
        }
    }

The order by can then be called as follows:

query = query.OrderBy("ProductName");