How to add the existing site column to the Content type in SharePoint

In this article we will be seeing how to add the existing site column to the content type in SharePoint.

Adding a existing site column to the content type using powershell script

$site = Get-SPSite -Identity "http://serverName:4001/"
$web = $site.RootWeb

$ct=$web.ContentTypes["_Custom Content Type"];
$fieldAdd=$web.Fields["Custom Site Column"]
$fieldLink=New-Object Microsoft.SharePoint.SPFieldLink($fieldAdd)
$ct.FieldLinks.Add($fieldLink);
$ct.Update()

$web.Dispose()
$site.Dispose()

The existing content type "Custom Site column" is added to the content type "_Custom Content Type".

Adding a existing site column to the content type using C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.SharePoint;

namespace Testing
{
class Program
{
static void Main(string[] args)
{
using (SPSite site = new SPSite("http://serverName:4001/"))
{
using (SPWeb web = site.RootWeb)
{
SPContentType ct = web.ContentTypes["_Custom Content Type"];
SPField field = web.Fields["Custom Site Column"];
SPFieldLink fieldLink = new SPFieldLink(field);
ct.FieldLinks.Add(fieldLink);
ct.Update();
}
}
}
}
}

$site = Get-SPSite -Identity "http://serverName:4001/"
$web = $site.RootWeb
$field=$web.Fields["Custom Site Column"]
$field.Type= "Choice"
$field.Update($true)
$web.Dispose()
$site.Dispose()

The property of the existing site column is changed from "Text" to "Choice".