C# 表達式樹分頁擴展（三）

時間 2019-11-18

標籤 c# 表達式分頁擴展欄目 C# 简体版

原文原文鏈接

1、前言

前面咱們知道了表達樹的基本知識，也明白了怎麼遍歷和修改一個表達式，這裏咱們就一個實際的場景來進行功能開發。html

表達式系列目錄算法

C# 表達式樹講解（一）sql

C# 表達式樹遍歷（二）數據庫

C# 表達式樹分頁擴展（三）app

C# 表達式樹Lambda擴展（四）ide

2、分頁擴展

在實際的開發中，確定會遇到這樣的應用場景，一個數據源須要在頁面上進行分頁顯示，而且頁面上須要對該數據源有一個排名。原本分頁能夠在數據庫層面完成，可是由於這裏有一個排名功能，所謂的排名，就是須要查詢出全部知足條件的數據，而後按照某個算法升序或者降序排列，而後按照進行排名。排名以後，而後根據分頁信息，將當前頁的數據返回給頁面，固然中間還有自定義排序的因素。測試

怎麼取數據源和怎麼排序，這裏先不作介紹，咱們就實現對一個數據源分頁的功能。ui

咱們先定義好分頁的實體對象spa

分頁請求對象PageRequest.cs，由於在【ORM之Dapper運用】已經說明，因此這裏我就只粘貼處代碼code

public class PageRequest
    {
        /// <summary>
        /// 每頁條數
        /// </summary>
        public int PageSize { get; set; }

        /// <summary>
        /// 當前頁數
        /// </summary>
        public int PageIndex { get; set; }

        /// <summary>
        /// 排序字段
        /// </summary>
        public string SortBy { get; set; }

        /// <summary>
        /// 排序方式（desc、asc）
        /// </summary>
        public string Direction { get; set; }

        /// <summary>
        /// 獲取排序sql語句
        /// </summary>
        /// <returns></returns>
        public string GetOrderBySql()
        {
            if (string.IsNullOrWhiteSpace(SortBy))
            {
                return "";
            }
            var resultSql = new StringBuilder(" ORDER BY ");
            string dir = Direction;
            if (string.IsNullOrWhiteSpace(dir))
            {
                dir = "ASC";
            }
            if (SortBy.Contains("&"))
            {
                resultSql.Append("").Append(string.Join(",", SortBy.Split('&').Select(e => $" {e} {dir}").ToArray()));
            }
            else
            {
                resultSql.Append(SortBy).Append("").Append(dir);//默認處理方式
            }
            return resultSql.ToString();
        }
    }

View Code

分頁的返回對象PageResponse.cs

/// <summary>
    /// 通用分頁返回
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class PageResponse<T>
    {
        /// <summary>
        /// 總條數
        /// </summary>
        public long TotalCount { get; set; }

        /// <summary>
        /// 返回
        /// </summary>
        public List<T> Items { get; set; }

        /// <summary>
        /// 當前頁
        /// </summary>
        public long PageIndex { get; set; }

        /// <summary>
        /// 每頁條數
        /// </summary>
        public long PageSize { get; set; }

        /// <summary>
        /// 總頁數
        /// </summary>
        public long TotalPages { get; set; }

        /// <summary>
        /// 返回篩選集合
        /// </summary>
        public Dictionary<string, List<string>> ResultFilter = new Dictionary<string, List<string>>();

    }

View Code

對數據集分頁方法的實現

public class PFTPage
    {
        /// <summary>
        /// 對數據集分頁
        /// </summary>
        /// <typeparam name="T">數據集對象</typeparam>
        /// <param name="source">數據集</param>
        /// <param name="page">分頁信息</param>
        /// <returns></returns>
        public static PageResponse<T> DataPagination<T>(IQueryable<T> source, PageRequest page) where T : class, new()
        {
            var sesultData = new PageResponse<T>();
            bool isAsc = page.Direction.ToLower() == "asc" ? true : false;
            string[] _order = page.SortBy.Split('&');
            MethodCallExpression resultExp = null;
            foreach (string item in _order)
            {
                string _orderPart = item;
                _orderPart = Regex.Replace(_orderPart, @"\s+", "");
                string[] _orderArry = _orderPart.Split(' ');
                string _orderField = _orderArry[0];
                bool sort = isAsc;
                if (_orderArry.Length == 2)
                {
                    isAsc = _orderArry[1].ToUpper() == "ASC" ? true : false;
                }
                var parameter = Expression.Parameter(typeof(T), "t");
                var property = typeof(T).GetProperty(_orderField);
                var propertyAccess = Expression.MakeMemberAccess(parameter, property);
                var orderByExp = Expression.Lambda(propertyAccess, parameter);
                resultExp = Expression.Call(typeof(Queryable), isAsc ? "OrderBy" : "OrderByDescending", new Type[] { typeof(T), property.PropertyType }, source.Expression, Expression.Quote(orderByExp));
            }
            var tempData = source.Provider.CreateQuery<T>(resultExp);
            sesultData.PageIndex = page.PageIndex;
            sesultData.PageSize = page.PageSize;
            sesultData.TotalCount = tempData.Count();

            sesultData.TotalPages = sesultData.TotalCount / sesultData.PageSize;
            if (sesultData.TotalCount % sesultData.PageSize > 0)
            {
                sesultData.TotalPages += 1;
            }

            sesultData.Items = tempData.Skip(page.PageSize * (page.PageIndex - 1)).Take(page.PageSize).ToList();
            return sesultData;
        }
    }

爲了測試，咱們定義一個學生課程成績的測試類

public class ScoreClass
{
    public string CourseName { get; set; }
    public string StudentName { get; set; }
    public decimal Score { get; set; }
}

調用代碼

var datas = new List<ScoreClass>();
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生A",
                Score = 60
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生B",
                Score = 65
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生C",
                Score = 70
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生D",
                Score = 75
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生E",
                Score = 80
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生F",
                Score = 81
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生G",
                Score = 82
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生H",
                Score = 83
            });
            datas.Add(new ScoreClass
            {
                CourseName = "數學",
                StudentName = "學生I",
                Score = 84
            });
            //按照Score降序排序取第一個（5條數據）
            var page = new PageRequest()
            {
                Direction= "desc",
                PageIndex=1,
                PageSize=5,
                SortBy= "Score"
            };
            var result = PFTPage.DataPagination(datas.AsQueryable(), page);

            Console.WriteLine($"分頁結果：\n{string.Join("\n", result.Items.Select(e=>$"{e.StudentName} {e.CourseName} {e.Score}"))}");