ClientContext ctx = new ClientContext(weburl); ctx.Credentials = new SharePointOnlineCredentials(userName, passWord); List list = ctx.Web.Lists.GetByTitle("ListTitle"); ListItem currentItem = list.GetItemById(1); FieldUserValue[] userValueCollection = new FieldUserValue[1]; //Get all the users of this Web UserCollection userCollection = this.ctx.Web.SiteUsers; this.ctx.Load(userCollection, w => w.Include(p => p.Id, p => p.Title)); this.ctx.ExecuteQuery(this.ctx); User user = userCollection.FirstOrDefault(p => p.Title.ToLower().Trim() == userTitle.ToLower().Trim()); //Making sure that a user of title userTitle is present in this Web if (user != null) { FieldUserValue fieldUserVal = new FieldUserValue(); fieldUserVal.LookupId = user.Id; userValueCollection.SetValue(fieldUserVal, 0); } currentItem["MultiUserValCol"] = userValueCollection; currentItem.Update(); this.ctx.ExecuteQuery();
As you can see that updating a multiUser column is along the same line as updating a LookupMulti column. Hence, there are a couple of things that one should take care of while updating this column. Those are mentioned in my previous blog where I have discussed about updating a LookupMulti column. here. https://realmpksharepoint.wordpress.com/2014/01/19/update-a-lookupmulti-column-value-in-sharepoint-using-client-object-model-c/