sdanna sdanna - 2 months ago 13
C# Question

Multiple Order By with LINQ

I start with a basic class that I want to manipulate in a List using LINQ, something like the following:

public class FooBar
{
public virtual int Id { get; set; }
public virtual string Foo{ get; set; }
public virtual string Bar{ get; set; }
}


This is what I ultimately found out to solve my problem using the non lambda LINQ stuff.

// code somewhere else that works and gets the desired results
var foobarList = GetFooBarList(); // Abstracted out - returns List<Foobar>

// Interesting piece of code that I want to examine
var resultSet = from foobars in foobarList
orderby foobars.Foo, foobars.Bar
select foobars;

// Iterate and do something interesting
foreach (var foobar in resultSet)
{
// Do some code
}


What I'm really curious about is if the same can be accomplished using the Lambda based extension methods off of generic IEnumerable to accomplish the same thing. Google tells me I can do something like the following to accomplish it

var resultSet = foobarList.OrderBy(x => new {x.Foo, x.Bar})
.Select(x=>x);


However if I do that I get a runtime error when I hit the foreach statement. The error tells me that at least one object has to implement IComparible, which I can see that since I'm using an anonymous type for the .OrderBy() method.

So is there a way to accomplish what I want using the Lambda way?

Answer

You can use the ThenBy and ThenByDescending extension methods:

foobarList.OrderBy(x => x.Foo).ThenBy( x => x.Bar)