public void Update <T>(T entity) where T : class, IAggregateRoot
{
if (entity == null)
{
throw new Exception("t is null");
}
_dragonDBContext.Set <T>().Attach(entity);//将数据附加到上下文，支持实体修改和新实体，重置为UnChanged
_dragonDBContext.Entry <T>(entity).State = EntityState.Modified;
}
