关于GridView分页的疑惑

前台页面Gridview的数据源为ObjectDataSource控件的数据：
<asp:ObjectDataSource ID="ObjectDataSource1" runat="server" SelectMethod="GetData"
        TypeName="ZWW.BLL.VideoDataSource" MaximumRowsParameterName="pageSize" StartRowIndexParameterName="startIndex"
        EnablePaging="True" SelectCountMethod="GetTotal" DeleteMethod="DeleteVideo">
        <SelectParameters>
            <asp:ControlParameter ControlID="ddl_courseId" Name="COURSE_ID" PropertyName="Text" />
            <asp:ControlParameter  ControlID="tb_videoname" Name="VideoName" Type="String"/>
        </SelectParameters>
        <DeleteParameters>
            <asp:Parameter Name="VIDEO_ID" Type="Int64" />
        </DeleteParameters>
    </asp:ObjectDataSource>分页方法的实现：
    [DataObject]
    public class VideoDataSource
    {
        [DataObjectMethod(DataObjectMethodType.Select, true)]
        public IEnumerable GetData(int startIndex, int pageSize, string VideoName, long COURSE_ID)
        {
            DataClassesDataContext db = DataClassesDataContext.Default;
            IQueryable<T_VIDEO> videos = db.T_VIDEO;
            if (!string.IsNullOrEmpty(VideoName))
            {                VideoName = VideoName.Trim();
                videos = videos.Where(u => u.VIDEO_NAME.Contains(VideoName));            }
            if (COURSE_ID != 0)
            {
                videos = videos.Where(v => v.COURSE_ID == COURSE_ID);
            }            var data = videos.Select(v => new
            {
                v.VIDEO_ID,
                v.VIDEO_NAME,
                v.VIDEO_URL,
                v.ORDER_ID,
                v.TIME_LENGTH,
                v.VIDEO_DESC,
                v.T_COURSE.COURSE_NAME
            }
            ).OrderBy(v => v.ORDER_ID).Skip(startIndex).Take(pageSize).ToArray();            return data;
        }        public int GetTotal(string VideoName, long COURSE_ID)
        {
            DataClassesDataContext db = DataClassesDataContext.Default;
            IQueryable<T_VIDEO> videos = db.T_VIDEO;
            if (!string.IsNullOrEmpty(VideoName))
            {                VideoName = VideoName.Trim();
                videos = videos.Where(u => u.VIDEO_NAME.Contains(VideoName));            }
            if (COURSE_ID != 0)
            {
                videos = videos.Where(v => v.COURSE_ID == COURSE_ID);
            }
            return videos.Count();
        }我很疑惑的就是[DataObject]和[DataObjectMethod(DataObjectMethodType.Select, true)]的作用。另外public IEnumerable GetData方法的返回类型如果改为IQueryable也是有问题的，这是为什么？？？求帮帮忙，小弟是新手