字典中的自定义键 [英] Custom key in dictionary
问题描述
你好，
我有一个以此产品类为密钥的字典。
private Dictionary< Product，long> _dictProduct = null;
publi class产品
{
$
public string ProductName {get;组; }
public string ProductCategory {get;组; }
}
public void MyMethod（string productName，string productCategory）
{
//
$
}
在这种方法中，我需要能够根据productName和productCategory从字典中检索相应的值。
如何实现这一目标？
Hello,
I've a dictionary with this Product class as key.
private Dictionary<Product, long> _dictProduct = null;
publi class Product
{
public string ProductName { get; set; }
public string ProductCategory { get; set; }
}
public void MyMethod(string productName, string productCategory)
{
//
}
In this method, I need to be able to retrieve the corresponding value from the dictionary based on productName and productCategory.
How do I achieve this please?
我是否需要制作在这里使用元组？
谢谢。
Do I need to make use of Tuple here?
Thanks.
推荐答案
这对你来说无关紧要。为了成为一个键，值必须是唯一可识别的（通过调用GetHashCode）。使用像Product这样的ref类型意味着每个实例都是它自己的键。那时你通过使用字典获得了什么。例如
这不起作用。
That isn't going to work out for you. In order to be a key the value has to be uniquely identifiable (by calling GetHashCode). Using a ref type like Product means every instance is its own key. At that point you gain nothing by using a dictionary. For example this won't work.
var product1 = new Product() { ProductName = "A",
ProductCategory = "1" };
var product2 = new Product() { ProductName = "B", ProductCategory = 2" };
_dictProduct[product1] = 1;
_dictProduct[product2] = 2;
//Now if you try this
var product = new Product() { ProductName = "A", ProductCategory = "1" };
//Not found
var id = _dictProduct[product];
引用类型（字符串和其他非常特殊格式的类型除外）并不是真正设计为键。因此，在您按名称和类别查找产品的示例中，您将无法进行字典提供的常量时间查找。
您将拥有的唯一选项是枚举整个键列表。列表<产品>会有相同的行为，并会以你想要的方式工作。
Reference types (other than strings and other very specially formatted types) are not really designed to be keys. So in your example of finding a product by name and category, you aren't going to be able to do the constant time lookup that a dictionary provides. The only option you'll have is to enumerate the entire list of keys. A List<Product> would have the same behavior and would work the way you want.
所以，在你的例子中，我只使用List< Product>与LINQ结合使用。如果您确实需要将这两个值组合成一个复合键，那么创建一个简单的结构（而不是类）并在那里设置它们。然后实现IEquatable< T>，Object.Equals，
C＃相等运算符，GetHashCode等，以正确实现struct的相等性。请注意，您的结构必须是不可变的，因为您的相等逻辑必须将它们两者合并为一个哈希值，并且哈希值在
对象的生命周期内不能更改。如果确实如此，那么你将无法再找到它。
So, in your example, I'd just use List<Product> in combination with LINQ. If you really need to combine these 2 values into a composite key then create a simple struct (not class) and set them there. Then implement IEquatable<T>, Object.Equals, the C# equality operators, GetHashCode, etc to properly implement equality on the struct. Note that your struct must be immutable because your equality logic has to combine both of them into a hash value and the hash value cannot change for the life of the object. If it does then you won't be able to find it again.
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