Question

我正在尝试与Dictionary<>一起使用List<>进行搜索。我知道，我可以使用List<>轻松完成此操作，如下所示：

var con = (from c in db.Customers
           where c.Status == status
           select c).ToList();

但首选并尝试使用Dictionary<>实现上述功能。我的概念（我们都知道）使用键/值会增加搜索选项的性能。这看起来很简单并且有点卡住了。这是我尝试过的：

static void Main(string[] args)
{
   Dictionary<string, Customer> custDictionary = new Dictionary<string, Customer>(); //Dictionary declared

   List<Customer> lst = new List<Customer>(); //List of objects declared

   Customer aCustomer = new Customer(); //Customer object created

   /**Assign values - Starts**/
   aCustomer.CustomerId = 1001;
   aCustomer.CustomerName = "John";
   aCustomer.Address = "On Earth";
   aCustomer.Status = "Active";

   aCustomer.CustomerId = 1002;
   aCustomer.CustomerName = "James";
   aCustomer.Address = "On Earth";
   aCustomer.Status = "Inactive";
   /**Assign values - Ends**/

   custDictionary.Add(aCustomer.Status, aCustomer); //Added to the dictionary with key and value

   string status = Console.ReadLine().ToUpper();

   if (custDictionary.ContainsKey(status)) //If key found in the dictionary
   {
      Customer cust = custDictionary[status];
      Console.WriteLine(cust.CustomerId + " " + cust.CustomerName); //Outputs the final result - Right now no result found here
   }

  Console.ReadKey();
}

public class Customer
{
   public int CustomerId { get; set; }
   public string CustomerName { get; set; }
   public string Address { get; set; }
   public string Status { get; set; }
}

不幸的是，上述内容并未返回任何结果。我想要的是通过传递状态键获取客户详细信息，并再次传递Customer对象作为值。我不确定我在这里缺少什么。

还有一件事，在现实生活中，我们将数据库结果作为列表。所以在这种情况下，如果使用Dictionary<>，我相信，数据库结果应该保持如下：

lst.Add(aCustomer); //As database will have more result or data simply

另一方面，我相信，字典应该如下所示：

Dictionary<string, List<Customer>> custDictionary = new Dictionary<string, List<Customer>>();

我的问题 - 在密钥/值对中传递字典中的对象列表是一个好主意，我尝试过这样做。但是还没有得到输出。

注意：这听起来像是一个新手问题，是的，是的。我试图在网上搜索并仍在研究它。我道歉要问这样一个问题，如果有更好的方法可以做到这一点，我会期待一些答案。

Answer 1

<强>已更新

如果要将它们存储在列表中，可以执行以下代码。要选择项目，您可以使用Linq，这样您就不会在字典中出现重复值的问题：

        var lst = new List<Customer>(); //List of objects declared

        lst.AddRange(
            new List<Customer>() {
                new Customer()
                {
                    CustomerId = 1001,
                    CustomerName = "John",
                    Address = "On Earth",
                    Status = "Active"
                },
                new Customer()
                {
                    CustomerId = 1002,
                    CustomerName = "James",
                    Address = "On Earth",
                    Status = "Inactive"
                }
            }
        );

        var status = Console.ReadLine();
        var selected = lst.Where(x => x.Status.ToUpper() == status.ToUpper()).ToList();
        foreach (var item in selected)
        {
            Console.WriteLine(item.CustomerId + " " + item.CustomerName);
        }

更新2

如果要在字典中添加上述列表，可以执行以下操作：

var custDictionary = new Dictionary<string, List<Customer>>();

// the above code for the list

custDictionary.Add("keyname", lst);

原始回答

您只保存一个客户，因为您用第二个客户覆盖了第一个客户：

Dictionary<string, Customer> custDictionary = new Dictionary<string, Customer>();
List<Customer> lst = new List<Customer>();

// Add first customer
var aCustomer = new Customer()
{
    CustomerId = 1001,
    CustomerName = "John",
    Address = "On Earth",
    Status = "Active"
};
custDictionary.Add(aCustomer.Status.ToUpper(), aCustomer);

// Add second customer
var bCustomer = new Customer()
{
    CustomerId = 1002,
    CustomerName = "James",
    Address = "On Earth",
    Status = "Inactive"
};
custDictionary.Add(bCustomer.Status.ToUpper(), bCustomer);

此外，您需要将状态存储为大写，因为您正在检查状态是否以大写形式存在：

string status = Console.ReadLine().ToUpper();
if (custDictionary.ContainsKey(status)) //If key found in the dictionary
{
    Customer cust = custDictionary[status];
    Console.WriteLine(cust.CustomerId + " " + cust.CustomerName); //Outputs the final result - Right now no result found here
}

Console.ReadKey();

Answer 2

即使您将状态添加为密钥，代码也会出现2个问题。

您需要创建2个对象，逐个创建2个客户。您只需添加一次客户，并分配两次值。
Console.ReadLine().ToUpper() - 删除ToUpper()，因为您要以大小写混合的形式添加值。如果您想这样做，请使用StringComparer.InvariantCultureIgnoreCase初始化字典。

这对你有用。

Dictionary<string, Customer> custDictionary = new Dictionary<string, Customer>(StringComparer.InvariantCultureIgnoreCase); //Dictionary declared

   List<Customer> lst = new List<Customer>(); //List of objects declared

   Customer aCustomer = new Customer(); //Customer object created

   /**Assign values - Starts**/
   aCustomer.CustomerId = 1001;
   aCustomer.CustomerName = "John";
   aCustomer.Address = "On Earth";
   aCustomer.Status = "Active";
   custDictionary.Add(aCustomer.Status, aCustomer); //Added to the dictionary with key and value

   Customer bCustomer = new Customer(); //Customer object created
   bCustomer.CustomerId = 1002;
   bCustomer.CustomerName = "James";
   bCustomer.Address = "On Earth";
   bCustomer.Status = "Inactive";


   custDictionary.Add(bCustomer.Status, bCustomer); //Added to the dictionary with key and value

   string status = Console.ReadLine().ToUpper();

   if (custDictionary.ContainsKey(status)) //If key found in the dictionary
   {
      Customer cust = custDictionary[status];
      Console.WriteLine(cust.CustomerId + " " + cust.CustomerName); //Outputs the final result - Right now no result found here
   }

  Console.ReadLine();

Answer 3

首先，你的字典键应该是customerId not status。检查字典是否包含密钥是一个很好的做法，它会抛出异常，同时添加相同的密钥。所以最好检查然后在字典中执行添加或更新。

static void Main(string[] args)
{
   Dictionary<string, Customer> custDictionary = new Dictionary<string, Customer>(); //Dictionary declared

   List<Customer> lst = new List<Customer>(); //List of objects declared

   Customer aCustomer = new Customer(); //Customer object created

   /**Assign values - Starts**/
   aCustomer.CustomerId = 1001;
   aCustomer.CustomerName = "John";
   aCustomer.Address = "On Earth";
   aCustomer.Status = "Active";
   if (!custDictionary.ContainsKey(aCustomer.CustomerId))
        custDictionary.Add(aCustomer.CustomerId, aCustomer);
    else
        custDictionary[aCustomer.CustomerId] = aCustomer;

   aCustomer.CustomerId = 1002;
   aCustomer.CustomerName = "James";
   aCustomer.Address = "On Earth";
   aCustomer.Status = "Inactive";
   /**Assign values - Ends**/

   if (!custDictionary.ContainsKey(aCustomer.CustomerId))
        custDictionary.Add(aCustomer.CustomerId, aCustomer);
    else
        custDictionary[aCustomer.CustomerId] = aCustomer;


   string status = Console.ReadLine().ToUpper();

   if (custDictionary.ContainsKey(aCustomer.CustomerId)) //If key found in the dictionary
   {
      Customer cust = custDictionary[aCustomer.CustomerId];
      Console.WriteLine(cust.CustomerId + " " + cust.CustomerName); //Outputs the final result - Right now no result found here
   }

  Console.ReadKey();
}

Answer 4

您没有获得任何输出，因为您将输入转换为大写，而您在pascalcase中插入了键，并且在C＃集合键的情况下区分大小写。这样你的输入就不会与集合中的任何键匹配

将您的行号更改为：29到此代码

 string status = Console.ReadLine();

并从您的控制台插入“非活动”，此密钥存在于您的集合中所以你会想要结果..

Answer 5

如果已经拥有该列表，并且想要创建一个Dictionary<string, List<Customer>>，您可以这样做：

Dictionary<string, List<Customer>> dict = 
        list.GroupBy(c=>c.Status.ToUpper()).ToDictionary(g => g.Key, g=> g.ToList());

迭代它：

foreach (var customer in dict[status.ToUpper()])
{
}

<强>但是，

我没有看到这样做的价值。如果你需要让具有特定状态的所有客户保持你所拥有的 - 一个简单的linq查询。

使用字典键/值对实现对象列表

5 个答案: