EF部分字段更新，忽略为null字段

public T Update<T>(T entity) where T : ModelBase
        {
            var set = this.Set<T>();
            set.Attach(entity);
            this.Entry<T>(entity).State = EntityState.Modified;
            this.SaveChanges();
            return entity;
        }

public T Update2<T>(T entity) where T : ModelBase
        {
            var set = this.Set<T>();
            set.Attach(entity);
            foreach (System.Reflection.PropertyInfo p in entity.GetType().GetProperties())
            {
                if (p.GetValue(entity) != null)
                {
                    this.Entry<T>(entity).Property(p.Name).IsModified = true;
                }
            }
            this.SaveChanges();
            return entity;
        }