How to enforce unique value for a column in SharePoint 2010 using powershell

In this article we will be seeing how to enforce unique value for a list or library column in SharePoint 2010 using C# and powershell.

In SharePoint 2010 we can enforce uniqueness on values in a list or library column, effectively creating a primary key. When you create a column in the list or library you could see an option "Enforce Unique Values" where you can enforce uniqueness. When you enforce uniqueness on a Lookup column, the list item in the target list can have only one list item looking up to it from the child list.

Using C#:

• Open Visual Studio 2010.
• Create Console application.
• Replace the code with the following.
  
  using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using Microsoft.SharePoint;

  namespace EnforceUniqueValue
  {
      class Program
      {
          static void Main(string[] args)
          {
              using (SPSite site = new SPSite("http://serverName:1111/"))
              {
                  using (SPWeb web = site.RootWeb)
                  {
                      SPList list = web.Lists.TryGetList("cl");
                      SPField field = list.Fields["TestCol"];
                      field.Indexed = true;
                      field.EnforceUniqueValues = true;
                      field.Update();
                  }
              }
          }
      }
  }
   

• Hit F5.
  
  
  
  Using PowerShell:
  
  $siteURL="http://serverName:1111/"
  $listName="cl"
  $fieldName="TestCol"
  $site=Get-SPSite $siteURL
  $web=$site.RootWeb
  $list=$web.Lists.TryGetList($listName)
  $field=$list.Fields[$fieldName]
  $field.Indexed=$true
  $field.EnforceUniqueValues=$true
  $field.Update()