//插入Topic表一条新纪录
public long Insert(long seminarId, Topic topic)
{
Seminar s = _db.Seminar.SingleOrDefault(c => c.Id == seminarId);
topic.Seminar = s;
try
{
_db.Attach(topic);
_db.Topic.Add(topic);
_db.SaveChanges();
long id = topic.Id;
return(id);
}
catch (System.Exception e)
{
throw e;
}
}