[英]Get top result in each parent property in Entity Framework
我试图选择每个部门中报告最多的员工。 我无法弄清楚如何使用Entity Framework中的LINQ做到这一点。 我使用的是EF Core,但答案应与EF 6相同,因此任一答案都可以。 我知道我需要使用.Distinct()
,但是我不确定如何正确使用它。
如何获得每个部门中报告最多的员工? 该查询应返回员工列表(或可查询)。
public class Employee
{
public long Id { get; set; }
public string Name { get; set; }
public long DepartmentId { get; set; }
public Department Department { get; set; }
public ICollection<Report> Reports { get; set; }
}
public class Department
{
public long Id { get; set; }
public string Name { get; set; }
public ICollection<Employee> Employees { get; set; }
}
这就是我的开始,但是我不确定这是否是正确的开始方式。
var employees = _context.Employees
.OrderByDescending(e => e.Reports.Count)
// ?
只需从每个部门中获取报告最多的员工即可:
var employees = _context.Departments.Select(department =>
department.Employees.OrderByDescending(employee => employee.Reports.Count).FirstOrDefault()).ToList();
您应该在部门级别开始查询。 在每个部门内,让其员工拥有最高的报告数量:
var topEmpPerDep = _context.Departments
.Select(dep => new
{
Department = dep.Name,
Employee = dep.Employees.OrderByDescending(e => e.Reports.Count)
.FirstOrDefault().Name
});
尝试这个 :
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var results = Department.departments.Select(x => new {
deptmentName = x.Name,
maxEmployeeReports = x.Employees.Select(y => new { name = y.Name, count = y.Reports.Count, employee = y }).OrderByDescending(z => z.count).FirstOrDefault()
}).ToList();
}
}
public class Employee
{
public long Id { get; set; }
public string Name { get; set; }
public long DepartmentId { get; set; }
public Department Department { get; set; }
public ICollection<Report> Reports { get; set; }
}
public class Department
{
public long Id { get; set; }
public string Name { get; set; }
public ICollection<Employee> Employees { get; set; }
public static List<Department> departments = new List<Department>();
}
public class Report
{
}
}
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