Question

I use this piece of code (found on stackoverflow) to generate an “OrderBy”

static class BuilderOrder
{
    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "OrderBy");
    }

    public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "OrderByDescending");
    }

    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "ThenBy");
    }

    public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
    {
        return ApplyOrder<T>(source, property, "ThenByDescending");
    }

    static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
    {
        string[] props = property.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);

        object result = 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[] { source, lambda });
        return (IOrderedQueryable<T>)result;
    }
}

I have this object :

public class Person : IPerson
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

public interface IPerson
{
    int Id { get; set; }
    string FirstName { get; set; }
    string LastName { get; set; }
}

It’s use like this

private void Tri(IQueryable<IPerson> list, string field, string direction)
{
    if (direction.ToUpper() == "DESC")
    {
        return BuilderOrder.OrderByDescending(liste, field);
    }
    else
    {
        return BuilderOrder.OrderBy(liste, field);
    }
}

The problem, the sorting is not working.
I’d like a way to send as parameter, the list to sort IQueryable<IPerson>, better IQueryable<T>, the fieldname (for sorting) and the direction (asc/desc)

Any idea ?

Thanks,

Answer 1

I can believe it’s not working… as you work in a void Method, without ref parameter !

Put your method Tri (rename it to SortBy or some English name would be better) in the BuilderOrder class and

public static IOrderedQueryable<T> SortBy(this IQueryable<T> queryable, string field, string direction)
{
    return (direction.ToUpper() == "DESC") 
       ? queryable.OrderByDescending(field)
       : queryable.OrderBy(field);
}

and you could add another one :

public static IOrderedQueryable<T> SortThenBy(this IOrderedQueryable<T> orderedQueryable, string field, string direction)
{
    return (direction.ToUpper() == "DESC") 
       ? orderedQueryable.ThenByDescending(field)
       : orderedQueryable.ThenBy(field);
}