C#按LastID进行分页——与lambda形成链式

Posted 2020-06-14

    public static class PageHelper
    {
        /// <summary>
        /// 按页码分页
        /// </summary>
        /// <param name="objects">要分页的数据集合</param>
        /// <param name="pageIndex">页码</param>
        /// <param name="pageSize">页大小</param>
        /// <returns></returns>
        public static object PageByIndex(this IEnumerable<object> objects, int pageIndex,int pageSize)
        {
            return objects.Skip(pageIndex * pageSize).Take(pageSize);
        }

        /// <summary>
        /// 获取当前项在列表中的位置
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="list"></param>
        /// <param name="item"></param>
        /// <param name="property"></param>
        /// <returns></returns>
        public static int GetPageIndex<T>(object[] list, object item, string property = "ID")
        {
            PropertyInfo ptyIdInfo = typeof(T).GetProperty(property);
            var index = 0;
            for (int i = 0; i < list.Length; i++)
            {
                var objid = ptyIdInfo.GetValue(list[i], null);
                if (Equals(objid, item))
                {
                    index = i;
                    break;
                }
            }
            return index;
        }

        /// <summary>
        /// 按lastid分页
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="objects">要分页的数据集合</param>
        /// <param name="item">分页项值</param>
        /// <param name="property">分页项</param>
        /// <param name="iswilful">分页项是最后一个还是任意中间一个</param>
        /// <param name="pageSize">页大小</param>
        /// <returns></returns>
        public static object PageByLastId<T>(this IEnumerable<object> objects, object item, bool iswilful= false,int pageSize=0, string property = "ID")
        {
            if(pageSize==0) pageSize = Int32.Parse(BaseHelper.GetValue("pageSize"));
            if (item==null||item.ToString()=="")
            {
                return objects.PageByIndex(0,pageSize);
            }
            var list = objects as object[] ?? objects.ToArray();
            var index = GetPageIndex<T>(list, item, property);
            if (iswilful)
            {
                return list.Skip(index + 1).Take(pageSize); //取任意ID后面pageSize条
            }
            else
            {
                if ((index + 1) % pageSize == 0)
                {
                    var pageIndex = index / pageSize + 1;
                    return PageByIndex(list, pageIndex,pageSize);
                }
                else
                {
                    return new List<T>();
                }   
            }
        }
    }

使用：

db.Database.SqlQuery<ScheduleDTO>(string.Format(sql,prjId,taskGroupId,userId)).PageByLastId<ScheduleDTO>(lastid)