How to add a Custom Column to a Site programmatically

Question

I'm programmatically creating Site Collections. The only thing I'd like to add to the newly created Site Collection are some Custom Columns that I've added manually in other examples..

The code I'm using is this:

 string SiteCollectionUrl = "/sites/Prova212222";

        Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(() =>
        {
            var Application = SPWebApplication.Lookup(new Uri("http://sp2010dev:44411/"));
            Application.Sites.Add(SiteCollectionUrl, "virtualsp\\Administrator", string.Empty, 1033, "STS#0", "virtualsp\\Administrator", "virtualsp\\Administrator", String.Empty);

            using (SPSite site = new SPSite("http://sp2010dev:44411" + SiteCollectionUrl))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    site.AllowUnsafeUpdates = true;
                    web.AllowUnsafeUpdates = true;

                    web.AvailableFields.Add("tt_content_id_padre", SPFieldType.Text, true);
                   //And so on for other columns
                }
            }
        });  

When I reach the Add method system raises this exception:

 This functionality is unavailable for field collections not associated with a list.

How can I solve this problem? I'm not interested in creating content type and so on, the only thing i need is the columns as I added manually!

Thank you

Answer 1

You should use SPWeb.Fields instead of SPWeb.AvailableFields

SPWeb.Fields are for the fields associated with this SPWeb
SPWeb.AvailableFields are for the fields available for this SPWeb or parents and is readonly

Here is an example of updating choices of a Choice Field using PowerShell:

$w = Get-SPWeb http://sp2010
$f = $w.Fields["pejaChoice"]
$f.Choices.Add("Testing")
$f.Update()

Answer 2

Use web.Fields.Add or better yet. Add them to the site collection fields like this: site.RootWeb.Fields.Add() and do a web.Update()

After that you can create ContentTypes, or add Fields to lists by getting the sitecolumns using web.AvailableFields["yourfield"].

Answer 3

Are you using any specific site template while creating the site, you may want to consider creating a feature that defines the site columns,

Then use the feature stapler to associate the site column feature with the site template.

This way you will be sure that the code may not fail for any reason.

Remember writing more code for doing this will increase the possiblity of failures.