Question

我需要在字典中实现两个键并且有点卡住了。我不确定它是否可行，但我的标准是使用两个键来匹配字典数据结构中的搜索选项，类似于下面的Linq：

if(id > 0 && status != null)
{
    var result = (from c in db.Employees
                  where c.EmployeeId == id && c.Status == status
                  select c).ToList();
}

使用词典，我尝试了以下内容：

public class Employee
{
   public int EmployeeId { get; set; }
   public string EmployeeName { get; set; }
   public string Address { get; set; }
   public string Status { get; set; }
}

public class TwoKeyDictionary<k1, k2, T> : Dictionary<k2, Dictionary<k2, T>>
{

}

最后尝试将Employee类与数据绑定并使用List＆lt;＆gt;为此：

List<Employee> employees = new List<Employee>()
{
    new Employee { EmployeeId = 1001, EmployeeName = "John", Address = "On Earth", Status = "Active"},
    new Employee { EmployeeId = 1002, EmployeeName = "Jack", Address = "On Earth", Status = "Active"},
    new Employee { EmployeeId = 1003, EmployeeName = "James", Address = "On Earth", Status = "Inactive"},
    new Employee { EmployeeId = 1004, EmployeeName = "Oswald", Address = "On Earth", Status = "Inactive"}
};

int id = 0;
string status = "" 

if (id > 0 && status != "")
{
    id = Convert.ToInt32(Console.ReadLine())
    status = Console.ReadLine().ToUpper();
}

TwoKeyDictionary<int, string, List<Employee>> dict = 
          employees.GroupBy(c => new { 
             CustomerId = c.EmployeeId, 
             c.Status })
         .ToDictionary(g => g.Key.CustomerId, g => g.Key.Status, g => g.ToList());

foreach (var item in dict[id][status])
{
    Console.WriteLine(item.CustomerId + " " + item.CustomerName); 
}

它看起来已经完成但是现在，我有例外，其中一个是：＆＃39; 无法转换为lambda表达式以键入System.Collections.Generic.IEComparer，因为它不是委托类型＆＃39; - ToDictionary（g =＆gt; g.Key.CustomerId，g =＆gt; g.Key.Status， g =＆gt; g.ToList（）。此行中的其他错误：var item in dict [id] [状态]。有没有办法摆脱它，可能在某处做错了。

Answer 1

我会将你的字典更改为：

Dictionary<Tuple<int, string>, List<Employee>>

因为你希望int和string都在一起并指定一个键。

此外，.ToDictionary调用如下所示：

Dictionary<Tuple<int, string>, List<Employee>> dict = 
    employees.ToDictionary(g => 
        new Tuple<int, string>(g.Key.CustomerId, g.Key.Status), g => g);

Answer 2

为什么不使用tuple作为密钥？

Dictionary<Tuple<K1, K2>, V> d1;

Answer 3

实际上你可以在没有额外课程的情况下完成这项课程，甚至只限于两个课程。使用匿名类型作为键的Lookup<TKey, TElement>：

var idStatusLookup = employees.ToLookup(x => new {x.EmployeeId, x.Status});
var matchingEmployees = idStatusLookup[new { EmployeeId = 1001, Status = "Active"}];

foreach (Employee emp in matchingEmployees)
{
    Console.WriteLine(emp.EmployeeId + " " + emp.EmployeeName);
}

查找类似于字典，但它允许有多个键，并且总是有一个值，即使对于非包含的键也是如此。怎么可能？如果未包含密钥，则返回Enumerable.Empty<TValue>，并返回相同密钥的值序列。

两个键和一个字典中的值

3 个答案: