Creating a sort function for a generic list

Question

I have a method for sorting generic lists by the object fields:

public static IQueryable<T> SortTable<T>(IQueryable<T> q, string sortfield, bool ascending)
{
    var p = Expression.Parameter(typeof(T), "p");

    if (typeof(T).GetProperty(sortfield).PropertyType == typeof(int?))
    {
        var x = Expression.Lambda<Func<T, int?>>(Expression.Property(p, sortfield), p);
        if (ascending)
            q = q.OrderBy(x);
        else
            q = q.OrderByDescending(x);
    }
    else if (typeof(T).GetProperty(sortfield).PropertyType == typeof(int))
    {
        var x = Expression.Lambda<Func<T, int>>(Expression.Property(p, sortfield), p);
        if (ascending)
            q = q.OrderBy(x);
        else
            q = q.OrderByDescending(x);
    }
    else if (typeof(T).GetProperty(sortfield).PropertyType == typeof(DateTime))
    {
        var x = Expression.Lambda<Func<T, DateTime>>(Expression.Property(p, sortfield), p);
        if (ascending)
            q = q.OrderBy(x);
        else
            q = q.OrderByDescending(x);
    }
    // many more for every type
    return q;
}

Is there any way I can collapse those ifs to a single generic statement? The main problem is that for the part Expression.Lambda<Func<T, int>> I am not sure how to write it generically.

stackoverflow.com/questions/41244/dynamic-linq-orderby

Marc Gravell
– Marc Gravell

2010-04-15 15:48:57 +00:00
Commented Apr 15, 2010 at 15:48 — Marc Gravell
– Marc Gravell, Commented Apr 15, 2010 at 15:48

dtb · Accepted Answer · 2010-04-15 15:52:27Z

3

If you expand Queryable.OrderBy to its definition then you don't have to use the generic overload of Expression.Lambda:

public static IQueryable<T> SortTable<T>(
    IQueryable<T> q, string sortfield, bool ascending)
{
    var p = Expression.Parameter(typeof(T), "p");
    var x = Expression.Lambda(Expression.Property(p, sortfield), p);

    return q.Provider.CreateQuery<T>(
               Expression.Call(typeof(Queryable),
                               ascending ? "OrderBy" : "OrderByDescending",
                               new Type[] { q.ElementType, x.Body.Type },
                               q.Expression,
                               x));
}

edited Apr 15, 2010 at 15:52

answered Apr 15, 2010 at 15:45

dtb

218k37 gold badges413 silver badges438 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Nayan · Accepted Answer · 2010-04-15 15:51:56Z

0

Won't this work?

    public static IQueryable<T> SortTable<T>(IQueryable<T> q, string sortfield, bool ascending)
    {
        var type = typeof(T).GetProperty(sortfield).PropertyType;
        var p = Expression.Parameter(typeof(T), "p");
        var x = Expression.Lambda<Func<T, type> >(Expression.Property(p, sortfield), p);
        if (ascending)
            q = q.OrderBy(x);
        else
            q = q.OrderByDescending(x);
        return q;
    }

answered Apr 15, 2010 at 15:51

Nayan

3,25429 silver badges35 bronze badges

3 Comments

dtb Over a year ago

type is not a type variable (like T), so this won't work.

Noldorin Over a year ago

There is a method in System.Reflection that can return the Func<T, type> type, however, I beleieve...

dtb Over a year ago

@Noldorin: Do you mean typeof(Func<,>).MakeGenericType(typeof(T), type)? But then you still cannot use the result to invoke Expression.Lambda<X> without reflection.

Collectives™ on Stack Overflow

Creating a sort function for a generic list

2 Answers 2

Comments

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related