从自定义集合项目的检索 [英] Retrieval of items from custom collection

问题描述

我有以下类

public class People
{
    public int id;
    public string nameHash;
    public string name;
}

我需要创建一个自定义集合，包括类的对象人，这让我找回它的 ID元素和 nameHash 。收集必须使用的foreach通过其元素进行迭代的能力：

I need to create a custom collection, consisting of objects of class People, that lets me retrieve elements by its id and nameHash. The collection must have the ability to iterate through its elements using foreach:

foreach (People person in PeopleCollection) { ... }

我该怎么办呢？如果你不能给一个详细的答案，至少给行动的简要计划。在此先感谢！

How do I do that? If you can not give a detailed answer, at least give a brief plan of action. Thanks in advance!

推荐答案

如果你在谈论一个大集合，你想基于一个整数更快的查找速度编号或字符串 NameHash 字段，同时还支持的foreach（富f由于fooCollection）模式，那么你就可以推出自己的集合，它封装了对字典。原油实现，而不是彻底的测试：

If you're talking about a large collection and you want faster lookups based on an integer Id or a string NameHash field while still supporting the foreach (Foo f in fooCollection) pattern, then you can roll your own collection that wraps a pair of dictionaries. Crude implementation, not thoroughly tested:

class Person
{
    public int Id { get; private set; }
    public string NameHash { get; private set; }
    public string Name { get; private set; }

    public Person(int id, string nameHash, string name)
    {
        Id = id;
        NameHash = nameHash;
        Name = name;
    }
}

class People : IEnumerable<Person>
{
    private Dictionary<int, Person> personDictionary = new Dictionary<int, Person>();
    private Dictionary<string, int> hashIdMap = new Dictionary<string, int>();

    public void Add(Person person)
    {
        if (person == null)
            throw new ArgumentNullException("person");

        if (personDictionary.ContainsKey(person.Id))
            throw new InvalidOperationException("person Id is already referenced in collection.");

        if (hashIdMap.ContainsKey(person.NameHash))
            throw new InvalidOperationException("person NameHash is already referenced in collection.");

        personDictionary.Add(person.Id, person);
        hashIdMap.Add(person.NameHash, person.Id);
    }

    public Person this[int id]
    {
        get
        {
            if (!personDictionary.ContainsKey(id))
                throw new ArgumentOutOfRangeException("Id is not in the collection.");

            return personDictionary[id];
        }
    }

    public Person this[string nameHash]
    {
        get
        {
            if (!hashIdMap.ContainsKey(nameHash))
                throw new ArgumentOutOfRangeException("NameHash is not in the collection.");

            return this[hashIdMap[nameHash]];
        }
    }

    public IEnumerator<Person> GetEnumerator()
    {
        foreach (KeyValuePair<int, Person> pair in personDictionary)
            yield return pair.Value;
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }
}

...

...

static void Main()
{
    Person personA = new Person(1, "A", "Apple");
    Person personB = new Person(2, "B", "Banana");
    Person personC = new Person(3, "C", "Cherry");

    People people = new People();
    people.Add(personA);
    people.Add(personB);
    people.Add(personC);

    Person foo = people[1];
    Person bar = people["C"];

    Debug.Assert(foo.Name == "Apple");
    Debug.Assert(bar.Name == "Cherry");

    foreach (Person person in people)
        Debug.WriteLine(person.Name);
}

当然，如果你正在处理一个小十岁上下的集合，很可能简单地使用列表< T> 和利用或者LINQ或查找方法已定义。如

Of course, if you're dealing with a small-ish collection, you could very well simply use a List<T> and utilize either LINQ or the Find methods already defined. Such as

Person personA = collection.FirstOrDefault(p => p.Id == 42);
Person personB = collection.Find(p => p.NameHash == "Blah");

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