c# - 我可以将同一对象添加到 LINQ 中的多个组吗？

Question

我想在 Linq 中对一组对象进行分组。然而我想使用的键是多个键的组合。例如

Object1: Key=SomeKeyString1

Object2: Key=SomeKeyString2

Object3: Key=SomeKeyString1,SomeKeyString2

现在我希望结果只有两组

Grouping1: Key=SomeKeyString1 : Objet1, Object3

Grouping2: Key=SomeKeyString2 : Object2, Object3

基本上我希望同一个对象属于两个组。这在 Linq 中可能吗？

Answer 1

嗯，不是直接使用GroupBy或GroupJoin。这两者都从对象中提取单个分组键。但是，您可以执行以下操作:

from groupingKey in groupingKeys
from item in items
where item.Keys.Contains(groupingKey)
group item by groupingKey;

示例代码:

using System;
using System.Collections.Generic;
using System.Linq;

class Item
{
    // Don't make fields public normally!
    public readonly List<string> Keys = new List<string>();
    public string Name { get; set; }
}

class Test
{
    static void Main()
    {
        var groupingKeys = new List<string> { "Key1", "Key2" };
        var items = new List<Item>
        {
            new Item { Name="Object1", Keys = { "Key1" } },
            new Item { Name="Object2", Keys = { "Key2" } },
            new Item { Name="Object3", Keys = { "Key1", "Key2" } },
        };

        var query = from groupingKey in groupingKeys
                    from item in items
                    where item.Keys.Contains(groupingKey)
                    group item by groupingKey;

        foreach (var group in query)
        {
            Console.WriteLine("Key: {0}", group.Key);
            foreach (var item in group)
            {
                Console.WriteLine("  {0}", item.Name);
            }
        }
    }
}