Lambda concatenation

Question

我試圖把我的lambda字符串與+標誌放在一起，它不會讓我運行代碼，因爲它說無效表達式！

頂端Code

的

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Threading.Tasks; 
using Microsoft.AspNetCore.Mvc; 
using Microsoft.AspNetCore.Mvc.Rendering; 
using Microsoft.EntityFrameworkCore; 
using Certifications.Data; 
using Certifications.Models; 
using Microsoft.EntityFrameworkCore.Internal; 

namespace Certifications.Controllers 
{ 
    public class Managerial : Controller 
    { 
     private readonly CertificationContext _context; 

     public Managerial(CertificationContext context) 
     { 
      _context = context; 
     } 

過濾

// Approval Filter 
string ApprovalFilterBuild = ""; 

if (approval == "Approved") 
{ 
    ApprovalFilterBuild = ".Where(i => i.Approved == true);"; 
} 

if (approval == "Revoked") 
{ 
    ApprovalFilterBuild = ".Where(i => i.Approved == false);"; 
} 

if (approval == "ALL") 
{ 
    ApprovalFilterBuild = ""; 
} 

查詢

var certificationContext = _context.INT_CertificationsXREF 
      .Include(i => i.INT_CertificationCategories) 
      .Include(i => i.INT_Certifications) 
      .Include(i => i.INT_CertificationConferred) 
      .Include(i => i.RIM_Resource) 
      +ApprovalFilterBuild+ 
      .Where(i => i.RIM_Resource.LAN == i.RIM_Resource.LAN) 
      .Where(i => LANlist.Contains(i.RIM_Resource.LAN)); 


return View(await certificationContext.ToListAsync()); 

Answer 1

批准過濾器需要是lambda表達式而不是字符串。這是你如何建立它。

// Approval Filter 
Expression<Func<INT_CertificationsXREF, bool>> ApprovalFilterBuild; 

if (approval == "Approved") 
{ 
    ApprovalFilterBuild = i => i.Approved == true; 
} 

if (approval == "Revoked") 
{ 
    ApprovalFilterBuild = i => i.Approved == false; 
} 

if (approval == "ALL") 
{ 
    ApprovalFilterBuild = i => true; 
} 

這就是你如何在主查詢中使用它。

var certificationContext = _context.INT_CertificationsXREF 
    .Include(i => i.INT_CertificationCategories) 
    .Include(i => i.INT_Certifications) 
    .Include(i => i.INT_CertificationConferred) 
    .Include(i => i.RIM_Resource) 
    .Where(ApprovalFilterBuild) 
    .Where(i => i.RIM_Resource.LAN == i.RIM_Resource.LAN) 
    .Where(i => LANlist.Contains(i.RIM_Resource.LAN)); 

如果批准，可沒有3個檢查，然後考慮將默認值i => true

Answer 2

所有這些LINQ的方法返回IQueryable<>實際上並不執行對您的數據庫中，直到你迭代結果。所以，你可以簡單地做這樣的事情：

//Assuming the type name is INT_CertificationsXREF: 
IQueryable<INT_CertificationsXREF> certificationContext = _context.INT_CertificationsXREF 
    .Include(i => i.INT_CertificationCategories) 
    .Include(i => i.INT_Certifications) 
    .Include(i => i.INT_CertificationConferred) 
    .Include(i => i.RIM_Resource); 

if (approval == "Approved") 
{ 
    certificationContext = certificationContext.Where(i => i.Approved == true); 
} 
else if (approval == "Revoked") 
{ 
    certificationContext = certificationContext.Where(i => i.Approved == false); 
} 

Answer 3

要確保它與兩個IEnumerable和IQueryable的，你可以使用下面的代碼：

var certificationContext = _context.INT_CertificationsXREF 
     .Include(i => i.INT_CertificationCategories) 
     .Include(i => i.INT_Certifications) 
     .Include(i => i.INT_CertificationConferred) 
     .Include(i => i.RIM_Resource).AsEnumerable(); 

if (approval == "Approved") 
{ 
    certificationContext = certificationContext.Where(i => i.Approved).AsEnumerable(); 
} 
if (approval == "Revoked") 
{ 
certificationContext = certificationContext.Where(i => !i.Approved).AsEnumerable(); 
} 
var result = certificationContext.Where(i => i.RIM_Resource.LAN == i.RIM_Resource.LAN).Where(i => LANlist.Contains(i.RIM_Resource.LAN)); 

的「結果」變量將有你想要的結果。