p2p.wrox.com Forums - Retrieving a single value from a single column in a single row?

Hi Ron,

You can use projection to select only the "column" or property of an object. You can then use FirstOrDefault (or First) to only get a single value. The following code would store Ron in the singleFirstName.FirstName variable:

Code:

 

Public Class Form1

  Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

    Dim list As New List(Of Person) From {New Person() With {.FirstName = "Imar", .LastName = "Spaanjaars"}, New Person() With {.FirstName = "Ron", .LastName = "Howerton"}}

    Dim singleFirstName = (From p In list

                          Where p.LastName = "Howerton"

                          Select New With {.FirstName = p.FirstName}).FirstOrDefault()

  ' singleFirstName.FirstName = Ron

  End Sub

End Class

Public Class Person

  Public Property FirstName As String

  Public Property LastName As String

End Class

This code "projects" the first name property into a new, anonymous object with a single property called FirstName.

You can also assign it to a string variable directly by just selecting the FirstName field, like this:

Code:

Dim singleFirstName = (From p In list

                          Where p.LastName = "Howerton"

                          Select p.FirstName).FirstOrDefault()

If you anticipate multiple results, drop the call to FirstOrDefault and loop over the values in singleFirstName (which then of course has an odd name ;-) ).

Hope this helps,

Imar