Sort a List using query expressions

Question

I have a problem using Linq to order a structure like this :

public class Person
{
    public int ID { get; set; }
    public List Attribu         


        

Answer 1

Some cases you need to consider:

• Since your attribute is in string an age of "30" and "3" will be ordered before an age of "4"
• The attribute might not exist

If you create this extension methods class:

public static class ListExtenstions
{
    public static List OrderList(this List list, string attributeName, PersonAttribute defaultAttribute)
    {
        return OrderList(list, attributeName, defaultAttribute, x => x);
    }

    public static List OrderList(this List list, string attributeName, PersonAttribute defaultAttribute, Func convertion)
    {
        return list.OrderBy(x => convertion((x.Attributes.FirstOrDefault(y => y.Name == attributeName) ?? defaultAttribute).Value)).ToList();

        // Query Syntax
        //return
        //    (from p in list
        //     let attribute = p.Attributes.FirstOrDefault(a => a.Name == attributeName) ?? defaultAttribute
        //     orderby attribute.Value
        //     select p).ToList();
    }
}

You can then sort the list correctly in this manner:

List persons = ...
...
PersonAttribute defaultAttribute = new PersonAttribute() { Value = "0" };
var ordered = persons.OrderList("Age", defaultAttribute, x => Convert.ToInt32(x));

This will give correct sorting order. If the attribute will always be present you could remove defaultAttribute.

To sort on 'Name' just use:

List persons = ...
...
PersonAttribute defaultAttribute = new PersonAttribute() { Value = String.Empty };
var ordered persons.OrderList("Name", defaultAttribute);