LINQ Group By Examples

These are 2 samples of  Group By Examples, one is very simple one but not simplest, second one is little bit intermediate. 

First creating a class to use in the given example

   1: Public Class TestRecord

   2:     Property ID As String

   3:     Property Value As String

   4:     Property RecordDate As Date

   5:  

   6:     Sub New()

   7:  

   8:     End Sub

   9:  

  10:     Sub New(ByVal id As String, ByVal value As String, ByVal recDate As Date)

  11:         Me.ID = id

  12:         Me.Value = value

  13:         Me.RecordDate = recDate

  14:     End Sub

  15: End Class

 

Now, let say use a button and Gridview to present the data on a page.

   1: Protected Sub Button4_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button4.Click

   2:         Dim showSimpleGroup As Boolean = False

   3:  

   4:         Dim lstItems As New List(Of TestRecord)

   5:         lstItems.Add(New TestRecord("1", "100", Now))

   6:         lstItems.Add(New TestRecord("2", "100", Date.MinValue))

   7:         lstItems.Add(New TestRecord("3", "100", #2/2/1980#))

   8:         lstItems.Add(New TestRecord("4", "200", Date.MinValue))

   9:         lstItems.Add(New TestRecord("5", "200", #1/1/2010#))

  10:         lstItems.Add(New TestRecord("6", "300", Now))

  11:  

  12:         If showSimpleGroup Then

  13:             Dim recList = From r In lstItems Group By r.Value Into g = Group Select New With {g, .ID = g.Max(Function(p) p.ID), .Value = g.Max(Function(p) p.Value)}

  14:             Me.gvwTest.DataSource = recList

  15:             Me.gvwTest.DataBind()

  16:         Else

  17:             Dim tempList = From d As TestRecord In lstItems Group By d.Value Into g = Group

  18:                             Select New With {g, .ID = g.Max(Function(d) d.ID), .RecordDate = g.Max(Function(d) IIf(d.RecordDate = Date.MinValue, Now, d.RecordDate))}

  19:  

  20:             If tempList IsNot Nothing AndAlso tempList.Count > 0 Then

  21:                 Dim recList = From r As TestRecord In lstItems Join t In tempList On t.ID Equals r.ID Select r

  22:                 Me.gvwTest.DataSource = recList

  23:                 Me.gvwTest.DataBind()

  24:             End If

  25:         End If

  26:     End Sub

 

The first grouping will display the distinct value excluding Record Date , second one will use the record’s max date to display the record the distinct value.

WCF Service Hosted in Web Farm or Multi-Homed Scenario

If a WCF Service is deployed in a load balanced environment and hosted on multiple Web Servers under IIS, which is accessed on a public domain, WCF WSDL document refers to a the responding machine name which is generally inaccessible on a public domain. So what you should be doing to make it right?

As per Microsoft, this design was initially designed in WCF but later when Microsoft went into Azure or Cloud Computing, this situation became an issue and realized the need to fix this problem. So in order to fix this problem, you need to perform two simple steps

1. Download the following Fix from Microsoft and Install on respective machines

                         http://code.msdn.microsoft.com/KB971842/Release/ProjectReleases.aspx?ReleaseId=3228

2. Add the following sections in behavior section of configuration

   1: <serviceBehaviors>

   2:    <behavior name="<name>">

   3:      <useRequestHeadersForMetadataAddress>

   4:        <defaultPorts>

   5:           <add scheme="http" port="80" />

   6:           <add scheme="https" port="443" />

   7:         </defaultPorts>

   8:       </useRequestHeadersForMetadataAddress>

   9:    </behavior>

  10: </serviceBehaviors>

  11:  

  12:  

For more information, you can checkout the following articles

a. http://support.microsoft.com/kb/980588

b. http://support.microsoft.com/kb/971842