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題前:,Select new{"需要的字段列.."}好處,減少不必要數據的查詢,尤其是分佈式的時候,網絡再不好的情況下,而不必要的數據又很多,Select new{"需要的字段列.."}好處明顯
如題,Linq多表鏈接分頁,Select new{"需要的字段列.."},配合楊濤Mvcpager,前臺遍歷展示自定義字段
(1) 我的例子是,(Tb_Mnager)管理員表與(Tb_Role)角色表聯查,返回兩個表部分字段的組合
如下控制器代碼:
public ActionResult List(int? pager)
{
pager = pager ?? 1;
int pageSize =20;
MyMvcCmsEntities db = new MyMvcCmsEntities();
//多表鏈接查詢,Select new{}返回需要的字段
//注意此處,rs實際會是一個List<Object>對象,如何在視圖中遍歷???答:反射
var rs = (from m in db.Tb_Manager
join r in db.Tb_Role on m.roleId equals r.id orderby m.sequeNum descending
select new
{
m.id,
//自定義的狀態,sql語句會轉化爲case..when..then
status = m.isDisable == 1 ? "<font color='red'>禁用</font>" : "<font color='green'>正常</font>",
m.loginName,
m.sequeNum,
m.date,
//角色表中的角色名字
r.roleName
});
//查詢總數----sql事件探查器可知:此處會查詢一次數據庫
ViewBag.allCount = rs.Count();
//本語句會自動生成select top....,並把結果List<Object>返回----此處會查詢二次數據庫
ViewBag.list = rs.ToPagedList((int)pager, pageSize);
return View();
}
(2) 好了,結果返回了,那麼前臺如何遍歷遍歷List<Object>的值呢?
答案:反射 詳情
C#反射的簡單應用 【注意】:.net4.0建議使用dynamic代替反射
此處,我用反射原理,寫了一個幫助類:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
namespace Mvc.Util
{
public class Reflection
{
/// <summary>
/// 獲取指定屬性的值(不區分大小寫)
/// </summary>
/// <param name="PropertyName">屬性名稱</param>
/// <param name="o">目標對象</param>
/// <returns></returns>
public static Object GetPropertyValueByName(string PropertyName, Object o)
{
if (o == null)
{
o = new { };
}
//創建一個返回對象
Object returnObject = new Object();
PropertyInfo[] p1 = o.GetType().GetProperties();
foreach (PropertyInfo pi in p1)
{
if (pi.Name.ToLower() == PropertyName.ToLower())
{
returnObject = pi.GetValue(o);
}
}
return returnObject;
}
}
}
(3) 這就好辦了,那麼我們在視圖View中遍歷並讀取值就簡單多了:
@{int index = 0;}
@foreach (Object t in ViewBag.list)
{
index++;
<tr>
<td align="center"><span class="checkall" style="vertical-align:middle;"><input class="list-box" value="@Reflection.GetPropertyValueByName("id", t).ToString()" type="checkbox" /></span></td>
<td>@index</td>
<td>@Reflection.GetPropertyValueByName("loginName", t).ToString()</td>
<td>
@Reflection.GetPropertyValueByName("roleName", t).ToString()
</td>
<td>@Reflection.GetPropertyValueByName("date", t).ToString()</td>
<td>
@Html.Raw(Reflection.GetPropertyValueByName("status", t).ToString())
</td>
<td>
<input type="text" value="@Reflection.GetPropertyValueByName("sequeNum", t).ToString()" class="sort" />
</td>
<td align="center"><a href='@Url.Action("edit", "manager", new { area="cms",id=Reflection.GetPropertyValueByName("id", t).ToString()})'>修改</a></td>
</tr>
}
視圖中分頁代碼,注意Html.Pager擴展方法第一個參數的類型爲IPagedList:
@Html.Pager((IPagedList)ViewBag.list, new PagerOptions { PageIndexParameterName = "pager", ShowPageIndexBox = false, PageIndexBoxType = PageIndexBoxType.TextBox, ShowGoButton = false, FirstPageText = "首頁", LastPageText = "尾頁", ShowFirstLast = true, CurrentPagerItemWrapperFormatString = "<span class=\"current\">{0}</span>", CssClass = "default" }, new { @style = "width:100%;float=left;" })