C# 字典：已添加具有相同键的项

在我的MVC应用程序中，我使用2个字典来填充DropDownList的SelectList。这些字典将提供日期作为字符串和日期时间值

我为第一本工作正常的词典编写了以下代码：

if (m_DictDateOrder.Count == 0)
{
     m_DictDateOrder = new Dictionary<string, DateTime>();
     m_DictDateOrder =
          m_OrderManager.ListOrders()
                        .OrderBy(x => x.m_OrderDate)
                        .Distinct()
                        .ToDictionary(x => x.m_OrderDate.ToString(), x => x.m_OrderDate);
}

我首先认为我添加了一个新的字典（这就是“新”出现的原因），但是没有。我做错了什么

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非常感谢

您将Distinct应用于订单，而不是日期。试一试

m_OrderManager.ListOrders()
                        .OrderBy(x => x.m_ShippedDate)
                        .Select(x =>x.m_ShippedDate)
                        .Distinct()
                        .ToDictionary(x => x.ToString(), x => x);

---

你在区分行，而不是日期

改为这样做：

if (m_DictDateShipped.Count == 0)
{
     m_DictDateShipped = m_OrderManager.ListOrders()
        //make the subject of the query into the thing we want Distinct'd.
        .Select(x => x.m_ShippedDate) 
        .Distinct()
        .ToDictionary(d => d.ToString(), d => d);
}

别费心分类了。字典是无序的

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我对此的标准模式（因为我不屑于使用Distinct）是：

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试一试，我会让你恢复成绩的。哇！就这么简单。非常感谢：）

ToDictionary

可能会再次破坏订单？

m_OrderManager.ListOrders()
                        .OrderBy(x => x.m_ShippedDate)
                        .Select(x =>x.m_ShippedDate)
                        .Distinct()
                        .ToDictionary(x => x.ToString(), x => x);

if (m_DictDateShipped.Count == 0)
{
     m_DictDateShipped = m_OrderManager.ListOrders()
        //make the subject of the query into the thing we want Distinct'd.
        .Select(x => x.m_ShippedDate) 
        .Distinct()
        .ToDictionary(d => d.ToString(), d => d);
}

dictionary = source
  .GroupBy(row => row.KeyProperty)
  .ToDictionary(g => g.Key, g => g.First()); //choose an element of the group as the value.