LINQ: Dynamic Order By clause

  • Thread starter Thread starter Armin Zingler
  • Start date Start date
A

Armin Zingler

Hi,

I'd like to order a query either by an Integer value or a String value.
I could write

select case condition
case 1
dim q = from bla in blub order by bla.IntegerProperty
case 2
dim q = from bla in blub order by bla.StringProperty
end select

This is of no use because I have to access q after "end select". But
if I declared it before "select case", I'd have to write

dim q as IOrderedEnumerable(Of TElement)

However, "TElement" is an anonymous type, so I can't do this also.

Is it possible to use a Comparer with the Order By clause anyhow?
Or, instead, can I achieve my goal by directly calling the extension method
System.Linq.Enumerable.OrderBy(Of TSource, TKey) anyhow?
In whichever direction I think, I always need the anonymous type. Probably
I do not and it's very simple, actually. Anybody's got a suggestion?
 
AZ> select case condition
AZ> case 1
AZ> dim q = from bla in blub order by bla.IntegerProperty
AZ> case 2
AZ> dim q = from bla in blub order by bla.StringProperty
AZ> end select

I'm not familiar with linq, but just as an idea from sql area that may be
useful here: you can do something like this in sql:

select column1 from table
order by
case
when column2='a' then column3
when column2='b' then column4
else column5
end
 
Armin said:
Hi,

I'd like to order a query either by an Integer value or a String value.
I could write

select case condition
case 1
dim q = from bla in blub order by bla.IntegerProperty
case 2
dim q = from bla in blub order by bla.StringProperty
end select

This is of no use because I have to access q after "end select". But
if I declared it before "select case", I'd have to write

dim q as IOrderedEnumerable(Of TElement)

However, "TElement" is an anonymous type, so I can't do this also.

Is it possible to use a Comparer with the Order By clause anyhow?
Or, instead, can I achieve my goal by directly calling the extension method
System.Linq.Enumerable.OrderBy(Of TSource, TKey) anyhow?
In whichever direction I think, I always need the anonymous type. Probably
I do not and it's very simple, actually. Anybody's got a suggestion?
Click to expand...

You should pull the data 'q' with no order by

This is C# example as close as I can get it. I don't have code in front
of me.

var a = q.orderacending(b => b.Property).Tolist();


I don't know if you have Lambda statement in VB.
 
Armin said:
Hi,

I'd like to order a query either by an Integer value or a String value.
I could write

select case condition
case 1
dim q = from bla in blub order by bla.IntegerProperty
case 2
dim q = from bla in blub order by bla.StringProperty
end select

This is of no use because I have to access q after "end select". But
if I declared it before "select case", I'd have to write

dim q as IOrderedEnumerable(Of TElement)

However, "TElement" is an anonymous type, so I can't do this also.

Is it possible to use a Comparer with the Order By clause anyhow?
Or, instead, can I achieve my goal by directly calling the extension method
System.Linq.Enumerable.OrderBy(Of TSource, TKey) anyhow?
In whichever direction I think, I always need the anonymous type. Probably
I do not and it's very simple, actually. Anybody's got a suggestion?
Click to expand...

You should pull the data 'q' with no order by

This is C# example as close as I can get it. I don't have code in front
of me.

var a = q.orderacending(b => b.Property).Tolist();


I don't know if you have Lambda statement in VB.
 
Mr. Arnold said:
You should pull the data 'q' with no order by

This is C# example as close as I can get it. I don't have code in front
of me.

var a = q.orderacending(b => b.Property).Tolist();


I don't know if you have Lambda statement in VB.
Click to expand...

I'm afraid, I can't read and translate this sCrabble# code. Thx anyway.
 
Armin said:
Hi,

I'd like to order a query either by an Integer value or a String value.
I could write

select case condition
case 1
dim q = from bla in blub order by bla.IntegerProperty
case 2
dim q = from bla in blub order by bla.StringProperty
end select

This is of no use because I have to access q after "end select". But
if I declared it before "select case", I'd have to write

dim q as IOrderedEnumerable(Of TElement)

However, "TElement" is an anonymous type, so I can't do this also.

Is it possible to use a Comparer with the Order By clause anyhow?
Or, instead, can I achieve my goal by directly calling the extension method
System.Linq.Enumerable.OrderBy(Of TSource, TKey) anyhow?
In whichever direction I think, I always need the anonymous type. Probably
I do not and it's very simple, actually. Anybody's got a suggestion?
Click to expand...

I got a reply (in the German group) that solves the problem. It says:

dim q = from bla in blub

select case condition
case 1
q = from bla in q order by bla.IntegerProperty
case 2
q = from bla in q order by bla.StringProperty
end select

'access q here

The trick is to assign the second query to the same variable as the first
one. Before, I wanted to assign it to another variable (q2) which created
the question of how to declare it.

Thx anyway for reading and replying.
 
I'm afraid, I can't read and translate this sCrabble# code. Thx anyway.
Click to expand...

I think the Mr. Arnold was implying something like this:

Option Explicit On
Option Strict On
Option Infer On

Module Module1
Dim rnd As New Random

Sub Main()
Dim lst As New List(Of TestClass)

For i As Integer = 1 To 100
lst.Add(New TestClass(rnd.Next(1, 101), Chr(rnd.Next(65, 91))))
Next

Dim orderByInt As Func(Of TestClass, Integer) = Function(x As TestClass) x.I
Dim orderByString As Func(Of TestClass, String) = Function(x As TestClass) x.S

Dim q As IEnumerable(Of TestClass) = From t In lst Select t

Console.WriteLine("======================== Order By Int ================")
For Each t In q.OrderBy(orderByInt)
Console.WriteLine("{0} : {1}", t.I, t.S)
Next
Console.ReadLine()
Console.WriteLine("======================== Order By string ================")
For Each t In q.OrderBy(orderByString)
Console.WriteLine("{0} : {1}", t.I, t.S)
Next

End Sub

Public Class TestClass
Public I As Integer
Public S As String

Public Sub New(ByVal i As Integer, ByVal s As String)
Me.I = i
Me.S = s
End Sub
End Class
End Module

HTH
 
Tom said:
I think the Mr. Arnold was implying something like this:

Option Explicit On
Option Strict On
Option Infer On

[...]
Click to expand...

Just wanted to say thank you so far only in the meantime because I haven't
read/tried it yet because the problem has been solved as mentioned in my other
replay.
 
Back
Top