Question

I would like to create a method that orders an IEnumerable List by a given property where the property is passed into the method by a string i.e. (Mind you the first code example does not work, but the second does and is what I am trying to emulate dynamically).

string sortName = "SerialNumber";
IEnumerable<PartSummary> partList = FunctionToCreateList();
partOrderedList = partList.OrderBy(what do I stick in here);

that would be equivalent to

IEnumerable<PartSummary> partList = FunctionToCreateList();
partOrderedList = partList.OrderBy(p => p.SerialNumber);

How can I accomplish this?

Answer 1

Are you saying you want to pass the order by in to your method? If so, you can use this:

Expression<Func<PartSummary, bool>> orderByClause

Then you can do this:

partOrderedList = partList.OrderBy(orderByClause);

Then you can handle your order by in your business layer or wherever you wish.

Okay, update: If you want to pass in the column name as a string you can do something like as follows:

Create a static class for an extension method (reference: http://social.msdn.microsoft.com/Forums/en-US/linqprojectgeneral/thread/39028ad2-452e-409f-bc9e-d1b263e921f6/):

static class LinqExtensions
{
    public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string sortingColumn, bool isAscending)
    {

        if (String.IsNullOrEmpty(sortingColumn))
        {
            return source;
        }

        ParameterExpression parameter = Expression.Parameter(source.ElementType, String.Empty);

        MemberExpression property = Expression.Property(parameter, sortingColumn);
        LambdaExpression lambda = Expression.Lambda(property, parameter);

        string methodName = isAscending ? "OrderBy" : "OrderByDescending";

        Expression methodCallExpression = Expression.Call(typeof(Queryable), methodName,
                                            new Type[] { source.ElementType, property.Type },
                                            source.Expression, Expression.Quote(lambda));

        return source.Provider.CreateQuery<T>(methodCallExpression);
    }
}

Then you can create your method:

   static IQueryable<PartSummary> FunctionToCreateList()
    {
        IList<PartSummary> list = new List<PartSummary>();
        list.Add(new PartSummary
                     {
                         Id = 1,
                         SerialNumber = "A",
                     });
        list.Add(new PartSummary
                     {
                         Id = 2,
                         SerialNumber = "B",
                     });
        return list.AsQueryable();
    }

And then call your method:

   static void Main(string[] args)
    {
        IQueryable<PartSummary> partOrderedList = FunctionToCreateList();
        PartSummary partSummary = new PartSummary();
        string sortBy = "Id";

        partOrderedList = partOrderedList.OrderBy(sortBy, false);

        foreach (PartSummary summary in partOrderedList)
        {
            Console.WriteLine(summary.Id + ", " + summary.SerialNumber);
        }
        Console.ReadLine();

    }

Now you can pass in the column name as a string and sort.

Hope this helps!