using string as an attribute for a linq query

Question

Possible Duplicate:
LINQ: orderby with dynamic string parameter

i'm sorting a IEnumarable with an OrderBy() clause. I'v a list with string with a value which contains the field I wanna order by. Now I'm using a switch statement for each property name.

  swich (propertyname)
    case "name":
      list = list.OrderBy(l=>l.name).ToList();
      break;
    case "property":
      list = list.OrderBy(l=>l.property).ToList();
      .....

is there a simple solution to use the string "propertyname" as an attribute in the orderby clause?

As I've done it I get an solution that is far from desirable. Not only is it more work to code each property, but if in the future any attribute is added this update wil be forgotten in the function i'm writing.

hope someone has got a better solution.

SimpleVar · Accepted Answer · 2012-05-02T11:51:07.053

3

var list = new List<MyClass>();

// Gets an object to give us access to the property with the given name of type MyClass
var propertyInfo = typeof(MyClass).GetProperty(propertyName);

// Each item is ordered by the value of the property
list = list.OrderBy(x => propertyInfo.GetValue(x, null)).ToList();

Explaining predicate:

var xPropVal = propertyInfo.GetValue(x, null);

Using the property info object, you get the value of the object x, with null parameters. The parameters will be used for indexers, in this case, since this is a property info object.

But since the properties in this case are all simple properties, the second parameter should be null or an empty object array.

edited May 02 '12 at 11:51

answered May 02 '12 at 11:38

SimpleVar

14,044
4
38
60

But how it will be if propertyname will have more variants? – Likurg May 02 '12 at 11:40
That's not what's being asked. The string is the name of the property, and there could be many more than 2. – yamen May 02 '12 at 11:40
The question implies that there are more than two properties. Note the dots in the end. – Stilgar May 02 '12 at 11:41
Edited to support multiple properties using reflection. – SimpleVar May 02 '12 at 11:43
@YoryeNathan Can you comment for me 'propertyInfo.GetValue(x, null)' please. – Likurg May 02 '12 at 11:47
@Likurg Let me know if more explaining is necessary. – SimpleVar May 02 '12 at 11:51

score 1 · Answer 2 · answered May 02 '12 at 11:40

1

The easiest way to do this is to look at he Dynamic Linq sample provided by Microsoft. Scott Guthrie has a blog post about it here: http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

The you can simply do this:

string propertyname = ...
list.OrderBy(propertyname).ToList();

answered May 02 '12 at 11:40

samjudson

56,243
7
59
69

You look at the comment of @dash? – Likurg May 02 '12 at 11:43
Yeah, and I agree with him, but I had already written my post by the time that came through :) – samjudson May 02 '12 at 11:44

using string as an attribute for a linq query

2 Answers2