LINQ查詢以獲取ASP.Net MVC 5應用程序中的計數

Question

在編寫LINQ查詢時需要幫助，以獲取基於部門的員工人數。

部門模式

public class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List<Employee> Employees { get; set; }
}

員工模式

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int DepartmentId { get; set; }
    public Department Department { get; set; }
}

MyViewModel

public class MyViewModel
{
    public string Department { get; set; }
    public int count { get; set; }
}

LINQ查詢

    public ActionResult shows()
    {
        //one department can have many employees and one employee can only be parrt of one department
        // below LINQ query fetches the count of employees belonging to each department
        var x = _context.Employees.Include("Department").GroupBy(e => e.DepartmentId)
     .Select(y=> new MyViewModel{
             Department= y.Key, // ERROR HERE AS Cannot type cast string to integer
            count = y.Count()               
        }).ToList();
     // code removed for brevity
        return Content("x");
    }

預期產量

Department                 Count (or employees)

Human Resource               10

Information Tech              5

問題如何編寫LINQ查詢以獲取上述輸出。 請指導我。

Answer 1

您有2個用於修改查詢的選項。 我假設您的Department模型包含要分配給視圖模型的Department屬性的屬性string Name 。

1. 獲取分組集合中的第一個Department ，並將其Name屬性分配給視圖模型Department屬性。 請注意，您需要添加.ToList()之前.GroupBy()以便查詢的第一部分是分組之前執行

    var x = _context.Employees .Include("Department") .ToList() .GroupBy(e => e.DepartmentId) .Select(y => new MyViewModel { Department = y.First().Department.Name, count = y.Count() }).ToList(); 

2. 將.GroupBy()表達式更改為按Department屬性的Name屬性分組

    var x = _context.Employees .Include("Department") .GroupBy(e => e.Department.Name) .Select(y=> new MyViewModel { Department = y.Key, count = y.Count() }).ToList(); 

Answer 2

public ActionResult shows()
    {
        //one department can have many employees and one employee can only be parrt of one department
        // below LINQ query fetches the count of employees belonging to each department
        var x = _context.Employees.Include("Department").GroupBy(e => new { e.DepartmentId, e.Department.Name})
     .Select(y=> new MyViewModel{
             Department= y.Key.Name
            count = y.Count()               
        }).ToList();
     // code removed for brevity
        return Content("x");
    }

這里的關鍵是按DepartmentId和名稱分組

Answer 3

像這樣嘗試：

public ActionResult shows()
{
    //one department can have many employees and one employee can only be parrt of one department
    // below LINQ query fetches the count of employees belonging to each department
    var x = _context.Employees.Include("Department").GroupBy(e => e.DepartmentId)
 .Select(y=> new MyViewModel{
         Department= y.Key.DepartmentName, // or whatever property you have for storing the name
        count = y.Count()               
    }).ToList();
 // code removed for brevity
    return Content("x");
}

Answer 4

您可以使用以下代碼：

using System.Linq;
using System.Web.Mvc;
using MvcApplication1.Models;

namespace MvcApplication1.Controllers
{
     
     public class HomeController : Controller
     {
          public ActionResult Index()
          {
               var dataContext = new MovieDataContext();
               int count = (from row in dataContext.Movies
                    where row.IsEnquiry == true
                 select row).Count();
               ViewBag.ItemCount = count;
               return View();
          }
     }
}