Assign new owner to appointment. “There should be only one owner party for an activity”

Question

I need to change the owner of an appointment record when creating a new appointment. I\'m using a plugin for the create message and i\'ve found this code to assign a new own

Answer 1

Guid id= new Guid("{33011A68-D311-E211-A429-005056820002}");    
 switch (context.MessageName)
                {
                    case "Update":
                        {
                            try
                            {
                                if (ent.Contains("fieldname") == true)
                                {

                                    AssignRequest assign = new AssignRequest
                                    {
                                        Assignee = new EntityReference("systemuser", id),
                                        Target = new EntityReference(ent.LogicalName, ent.Id)
                                    };
                                    _service.Execute(assign);
                                }
                            }
                            catch (Exception ex)
                            {
                                throw new InvalidPluginExecutionException("Error" + Environment.NewLine + "Details: " + ex.Message);
                            }
                        }
                        break;
                }