Sample how we can create relations for CMSImport on publish of an Umbraco content node

publishsample.cs

using System.Configuration;
using CMSImportLibrary.Helpers;
using Umbraco.Core;
using Umbraco.Core.Services;

namespace UpdateUmbracoRelations
{
    public class PublishedEventHandler : ApplicationEventHandler
    {
        protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            base.ApplicationStarted(umbracoApplication, applicationContext);
            ContentService.Published += ContentService_Published;
        }

        private void ContentService_Published(Umbraco.Core.Publishing.IPublishingStrategy sender, Umbraco.Core.Events.PublishEventArgs<Umbraco.Core.Models.IContent> e)
        {
            foreach (var publishedItems in e.PublishedEntities)
            {
                var relationKey = $"{ConfigurationManager.AppSettings["CMSImport.UmbracoRelationPrefix"]}{publishedItems.Id}";
                var id = DataHelper.GetRelatedIdFromRelation(relationKey,"Content");
                if (id == 0)
                {
                    //Relation does not exists, add it from this event
                    DataHelper.UpdateRelation(publishedItems.Id, relationKey, "Content");
                }
            }
        }
    }
}