構建ASP.NET MVC4+EF5+EasyUI+Unity2.x注入的後台管理系統（17）

LinQ動態排序

首先修復程序中的一個BUG這個BUG在GridPager類中,把sord修改為sort這個名稱填寫錯誤，會導致後台一直無法獲取datagrid的排序字段

本來是沒有這一講的,為了使20行的代碼精簡成2行,我查閱了一些資料,借鑒了一些大神的建議,首先感謝第八講中,11樓@nyth和15樓@紅顏醉丶帝的建議投遞，每一次的的排序要都一個判斷這的確很麻煩,我們利用反射來解決這個問題。

先看原來的代碼

//排序
            if (pager.order == "desc")
            {
                switch (pager.order)
                {
                    case "CreateTime":
                        queryData = queryData.OrderByDescending(c => c.CreateTime);
                        break;
                    case "Name":
                        queryData = queryData.OrderByDescending(c => c.Name);
                        break;
                    default:
                        queryData = queryData.OrderByDescending(c => c.CreateTime);
                        break;
                }
            }
            else
            {
    
                switch (pager.order)
                {
                    case "CreateTime":
                        queryData = queryData.OrderBy(c => c.CreateTime);
                        break;
                    case "Name":
                        queryData = queryData.OrderBy(c => c.Name);
                        break;
                    default:
                        queryData = queryData.OrderBy(c => c.CreateTime);
                        break;
                }
            }

以上每一次排序都要進行判斷,利用反射可以解決這個問題，我把他封裝起來了。（需要對反射有一些理解）

在App.Common中新建LinqHelper類代碼如下（下面有3個方法，我都對方法進行了注釋，看下就明白）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
    
namespace App.Common
{
   public class LinqHelper
    {
       /// <summary>
       /// 排序
       /// </summary>
       /// <typeparam name="T"></typeparam>
       /// <param name="source"></param>
       /// <param name="sortExpression"></param>
       /// <param name="sortDirection"></param>
       /// <returns></returns>
        public static IQueryable<T> DataSorting<T>(IQueryable<T> source, string sortExpression, string sortDirection)
        {
            string sortingDir = string.Empty;
            if (sortDirection.ToUpper().Trim() == "ASC")
                sortingDir = "OrderBy";
            else if (sortDirection.ToUpper().Trim() == "DESC")
                sortingDir = "OrderByDescending";
            ParameterExpression param = Expression.Parameter(typeof(T), sortExpression);
            PropertyInfo pi = typeof(T).GetProperty(sortExpression);
            Type[] types = new Type[2];
            types[0] = typeof(T);
            types[1] = pi.PropertyType;
            Expression expr = Expression.Call(typeof(Queryable), sortingDir, types, source.Expression, Expression.Lambda(Expression.Property(param, sortExpression), param));
            IQueryable<T> query = source.AsQueryable().Provider.CreateQuery<T>(expr);
            return query;
        }
       /// <summary>
       /// 分頁
       /// </summary>
       /// <typeparam name="T"></typeparam>
       /// <param name="source"></param>
       /// <param name="pageNumber"></param>
       /// <param name="pageSize"></param>
       /// <returns></returns>
        public static IQueryable<T> DataPaging<T>(IQueryable<T> source, int pageNumber, int pageSize)
        {
            if (pageNumber <= 1)
            {
                return source.Take(pageSize);
            }
            else
            {
                return source.Skip((pageNumber - 1) * pageSize).Take(pageSize);
            }
        }
       /// <summary>
        /// 排序並分頁 
       /// </summary>
       /// <typeparam name="T"></typeparam>
       /// <param name="source"></param>
       /// <param name="sortExpression"></param>
       /// <param name="sortDirection"></param>
       /// <param name="pageNumber"></param>
       /// <param name="pageSize"></param>
       /// <returns></returns>
        public static IQueryable<T> SortingAndPaging<T>(IQueryable<T> source, string sortExpression, string sortDirection, int pageNumber, int pageSize)
        {
            IQueryable<T> query = DataSorting<T>(source, sortExpression, sortDirection);
            return DataPaging(query, pageNumber, pageSize);
        }
    }
}

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