用于获取 ASP.Net MVC 5 应用程序中的计数的 LINQ 查询

Question

在编写 LINQ 查询以获取基于部门的员工数量时需要帮助。

部门模型

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

员工模型

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 查询

    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");
    }

预期输出

Department                 Count (or employees)

Human Resource               10

Information Tech              5

问题 如何编写 LINQ 查询以获取上述输出。请指导我。

Answer 1

您有 2 个选项可用于修改查询。我假设您的 Department 模型包含一个属性 string Name，您希望将其分配给您的视图模型的 Department 属性。

1. 获取分组集合中的第一个 Department 并分配其 Name 属性到您的视图模型 Department 属性。注意 您需要在 .GroupBy() 之前添加 .ToList() 以便 查询的第一部分在分组之前执行

   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. 将.GroupBy() 表达式更改为按Name 属性分组 Department 的属性

   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");
    }

这里的关键是按 DepartmentId AND Name 分组

Answer 3

试试这样：

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

您可以使用此代码：

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();
          }
     }
}