How can I use linq to sort by multiple fields?

Question

I\'m creating a mock data source that I want to be able to pass in a list of SortExpressions on.

public SortExpression(string name, SortDirection direction)
         


        

Answer 1

There are two problems. The first is the one others have alluded to - you need to use the value returned by OrderBy etc. The second is that each time you call OrderBy, that's adding a new "primary" ordering. You really want ThenBy after the first ordering has been applied. That makes it pretty ugly, unfortunately. It's still pretty ugly after a refactoring, but not too bad...

IEnumerable query = from item in items select item;
if (sortExpressionsExist)
{
    // Won't be read in the first iteration; will be written to
    IOrderedEnumerable orderedQuery = null;
    for (int i = 0; i < sortExpressions.Count; i++)
    {
        // Avoid single variable being captured: capture one per iteration.
        // Evil bug which would be really hard to find :)
        int copyOfI = i;
        // Tailor "object" depending on what GetProperty returns.
        Func expression = item => 
              item.GetType()
                  .GetProperty(sortExpressions[copyOfI].Name)
                  .GetValue(item, null);

        if (sortExpressions[i].Direction == SortDirection.Ascending)
        {
            orderedQuery = (i == 0) ? query.OrderBy(expression)
                                    : orderedQuery.ThenBy(expression);
        }
        else
        {
            orderedQuery = (i == 0) ? query.OrderByDescending(expression)
                                    : orderedQuery.ThenByDescending(expression);
        }
    }
    query = orderedQuery;
}