Create cross-site lookup fields in SharePoint 2010 utilizing site columns

This is documented on a few other blogs, including MSDN, but none of them were super clear.  Everyone processes information differently, so I hope this helps you out.  Please note that I’m using this code in my FeatureActivated even receiver.

This is handy when:

• You look up information in the same site collection
• You need to have one site column point at another site column in the same Site Collection, but across different web sites.

In my code, I refer to:

• SourceList (the list utilizing the site column where you are getting the information from)

Assume:

• New Column Name is the new site column I am creating in the current website
• Lookup Column Name is the existing site column, used in Source List, which lives in a different website /Subsite_Path_With_Source_List

In a nutshell, I am here:
/

and I want to look up information from this list:
/Subsite_Path_With_Source_List/Lists/Source List

Here is the code (update the items in bold and you should be all set):

using (SPWeb web = SPContext.Current.Web.Site.RootWeb)
{
    try
    {
        // Open the web containing the source list
        SPWeb webWithSourceList = SPContext.Current.Site.OpenWeb("Subsite_Path_With_Source_List");
        // Get the source list
        SPList lookupList = webWithSourceList.Lists["Source List"];
        // If it exists
        if (lookupList != null)
        {
            string lookupFieldName = "New Column Name";
            string sourceFieldName = "Lookup Column Name";
            web.Fields.AddLookup(lookupFieldName, lookupList.ID, webWithSourceList.ID, false);
            SPFieldLookup lookupField = (SPFieldLookup)web.Fields[lookupFieldName];
            lookupField.LookupField = lookupList.Fields[sourceFieldName].InternalName;
            lookupField.Update(true);

            myContentType.FieldLinks.Add(new SPFieldLink(lookupField));
            myContentType.Update();
        }
        // Dispose of the web
        webWithSourceList.Dispose();
    }
    catch (Exception)
    {
        throw;
    }
}