关于Linq的.distinct()方法的运用（一个简单的例子）

目的：在GroupDetail表里查询所有不重复的年级和科目，并保存在ArrayList里

在数据访问层

 internal class GroupDetailInfoDal : DaoImplements<int, GroupDetail>
    {
        internal GroupDetailInfoDal()
            : base("userCenter")
        {
        }

 　　 internal ArrayList GetGrade()
        {
            ArrayList arrayGrade = new ArrayList();
            var query = (from x in this.Table
                            where x.GradeID != 0
                           select x.GradeID).Distinct();
            if(query != null)

　　　　{
            　　var qq = query.ToList();
           　　 for (int i = 0; i < qq.Count; i++)
            　　{
                　　arrayGrade.Add(qq[i]);
            　　}

　　　　}
            return arrayGrade;
        }

        /// <summary>
        /// 查出所有科目编号
        /// </summary>
        /// <returns></returns>
        internal ArrayList GetSubject()
        {
            var query = (from n in this.Table
                         where n.SubjectID != 0
                         select n.SubjectID).Distinct();
           
            ArrayList arraySubject = new ArrayList();

 　　　　if (query != null)
            {
            　　var qq = query.ToList();
                  for (int i = 0; i < qq.Count;i++ )
                  {
                        arraySubject.Add(qq[i]);
                  }
            }
            return arraySubject;
        }

    }

接收：

　　  //得到导航所有内容
        void GetAllDetail()
        {
            //得到所有年级
            ArrayList arrayGrade = new ArrayList();   //年级编号
           
            arrayGrade = GroupDetailInfoBll.GetGrade();
            string Gname = "";
            for (int i = 0; i < arrayGrade.Count; i++)
            {
                Gname = GradeBll.Get(Convert.ToByte(arrayGrade[i])).Name;
                arrayGName.Add(Gname);
            }

            //得到所有科目
            ArrayList arraySuject = new ArrayList();  //科目编号
            arraySuject = GroupDetailInfoBll.GetSubject();
            string SName = "";
            for (int j = 0; j < arraySuject.Count; j++)
            {
                SName = SubjectBll.Get(Convert.ToInt16(arraySuject[j])).Name;
                arraySName.Add(SName);
            }
        }

就OK了！