我參考以下這一篇文章，想要做所謂的Dynamic LINQ：
http://kevintsengtw.blogspot.com/2012/06/dynamic-linq-entity-framework-part3.html
public ActionResult Test1()
{
using (NorthwindEntities db = new NorthwindEntities())
{
var query = db.Customers
.Where("City == @0 and Orders.Count >= @1", "London", 10)
.OrderBy("CustomerID desc")
.Take(10);
ViewData.Model = query.ToList();
return View();
}
}
然後我就把我的程式改寫成以下
public IPagedList<MemberViewModel> IPGetMemberToPaperRole(int ConferenceId, int PaperId, string Role, int? Page, string SearchKeyWord = "")
{
List<MemberViewModel> mv = new List<MemberViewModel>();
db.MemberToPapers.Where("ConferenceId == @0 AND PaperId == @1 AND Role == @2", ConferenceId, PaperId, Role)
.Join(db.Members.Where(wm => wm.Name.Contains(@3), SearchKeyWord),
m => m.MemberId,
x => x.MemberId,
(m, x) => new
{
m.ConferenceId,
m.PaperId,
m.Role,
x.MemberId,
x.Name,
x.Email
}).ToList()
.ForEach(o => mv.Add(new MemberViewModel
{
ConferenceId = o.ConferenceId,
PaperId = o.PaperId,
MemberId = o.MemberId,
Name = o.Name,
Email = o.Email,
RoleName = GetRole(o.Role)
}));
int pageNumber = (Page ?? 1);
int pageSize = 2;
return mv.ToPagedList(pageNumber, pageSize);
}
VS回報錯誤：'方法'Where'沒有任何多載使用4個引數'
不知道要如何修正才能改為Dynamic LINQ呢？
我想要做的是若SearchKeyWord有值，則搜尋出KeyWord相關的資料，若SearchKeyWord沒值，則搜尋出全部的資料。
已邀請的邦友 {{ invite_list.length }}/5
VS回報錯誤：'方法'Where'沒有任何多載使用4個引數'
不知道要如何修正才能改為Dynamic LINQ呢？
這是缺少套件原因,Dynamic LINQ是第三方NuGet套件,你需要安裝
安裝完後using就可以使用了
using System.Linq.Dynamic;
效果圖:
dynamic LINQ專案是開源的,可以看一下它使用的是DynamicExpression技術
所以有一個很重要概念它不只能用在LINQ SQL,普通的集合物件LINQ Object也可以使用,這是一個很強大的功能,舉例:
var datas = new[] { new { id = 1, value = "001" }, new { id = 2, value = "002" } };
var result = datas.AsQueryable().Where("id=@0", 1);
Console.WriteLine(result);
不過我覺得他的需求似乎並不需要Dynamic Linq。只要mv維持是IQueryable，然後根據條件再加入Where就好了，查詢並不需要一次做完。
IQueryable要等到Materialize時才會產生sql去跟資料庫查詢。（例如：呼叫ToList()方法等的時候）
fillano大大是的,他不需要使用到Dynamic LINQ,而且先熟悉強類型的LINQ更重要
其實想藉由他的提問跟大家介紹Dynamic LINQ不只能用在LINQ SQL的強大功能
如大大建議，是不用Dynamic Linq，改天再試做Dynamic Linq，不過目前改寫的內容只能用最笨的寫法如下：
if (!string.IsNullOrEmpty(SearchKeyWord))
{
db.MemberToPapers.Where(x => x.ConferenceId == ConferenceId && x.PaperId == PaperId && x.Role == Role)
.Join(db.Members.Where(wm => wm.Name.Contains(SearchKeyWord)),
m => m.MemberId,
x => x.MemberId,
(m, x) => new
{
m.ConferenceId,
m.PaperId,
m.Role,
x.MemberId,
x.Name,
x.Email
}).ToList()
.ForEach(o => mv.Add(new MemberViewModel
{
ConferenceId = o.ConferenceId,
PaperId = o.PaperId,
MemberId = o.MemberId,
Name = o.Name,
Email = o.Email,
RoleName = GetRole(o.Role)
}));
}
else
{
db.MemberToPapers.Where(x => x.ConferenceId == ConferenceId && x.PaperId == PaperId && x.Role == Role)
.Join(db.Members,
m => m.MemberId,
x => x.MemberId,
(m, x) => new
{
m.ConferenceId,
m.PaperId,
m.Role,
x.MemberId,
x.Name,
x.Email
}).ToList()
.ForEach(o => mv.Add(new MemberViewModel
{
ConferenceId = o.ConferenceId,
PaperId = o.PaperId,
MemberId = o.MemberId,
Name = o.Name,
Email = o.Email,
RoleName = GetRole(o.Role)
}));
}
嘗試著用fillano大大建議的方法，遇到許多轉型的問題。。。＞＜
var result = db.MemberToPapers.Where(x => x.ConferenceId == ConferenceId && x.PaperId == PaperId && x.Role == Role);
if (!string.IsNullOrEmpty(SearchKeyWord))
{
result = result.Join(db.Members.Where(wm => wm.Name.Contains(SearchKeyWord)),
m => m.MemberId,
x => x.MemberId,
(m, x) => new
{
m.ConferenceId,
m.PaperId,
m.Role,
x.MemberId,
x.Name,
x.Email
});
}
else
{
result = result.Join(db.Members,
m => m.MemberId,
x => x.MemberId,
(m, x) => new
{
m.ConferenceId,
m.PaperId,
m.Role,
x.MemberId,
x.Name,
x.Email
});
}
result.ToList()
.ForEach(o => mv.Add(new MemberViewModel
{
ConferenceId = o.ConferenceId,
PaperId = o.PaperId,
MemberId = o.MemberId,
Name = o.Name,
Email = o.Email,
RoleName = GetRole(o.Role)
}));
leo226 這段真的有重複代碼的壞味道
leo226 先Join db.Members，然後where下在if{}裡面啦。Don't repeat yourself。
fillano大大，其實先Join db.Members，然後where下在if{}裡面我知道，也很想，但改寫方式一直遇到錯誤，實在不知道該如何改，才只能用最爛的方式寫了。。。＞＜
如果大大方便的話是否可以給我一個小小範例，真的感激不盡～
var result = db.MemberToPapers.Where(x => x.ConferenceId == ConferenceId && x.PaperId == PaperId && x.Role == Role).Join(db.Members);
if (!string.IsNullOrEmpty(SearchKeyWord))
{
result = result.Where(wm => wm.Name.Contains(SearchKeyWord))
}
leo226 我用物件模擬你的資料：
https://dotnetfiddle.net/ISIiOl
你可以參考看看。
大大真的太用心了，我只要關鍵的小小範例，大大整個資料都模擬出來，我改寫如下測試OK了，非常感謝fillano花那麼多時間幫我解答，也感謝暐翰大師～謝謝～
var result = db.MemberToPapers.Where(x => x.ConferenceId == ConferenceId && x.PaperId == PaperId && x.Role == Role).Join(db.Members,
m => m.MemberId,
x => x.MemberId,
(m, x) => new
{
m.ConferenceId,
m.PaperId,
m.Role,
x.MemberId,
x.Name,
x.Email
});
if (!string.IsNullOrEmpty(SearchKeyWord))
{
result = result.Where(wm => wm.Name.Contains(SearchKeyWord));
}
result.ToList()
.ForEach(o => mv.Add(new MemberViewModel
{
ConferenceId = o.ConferenceId,
PaperId = o.PaperId,
MemberId = o.MemberId,
Name = o.Name,
Email = o.Email,
RoleName = GetRole(o.Role)
}));
iThome鐵人賽
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