LINQ:通过使它们可转换/可比较，对不同类型的集合使用.Except()吗? [英] LINQ: Use .Except() on collections of different types by making them convertible/comparable?

问题描述

给出两个不同类型的列表，是否有可能使这些类型在彼此之间可转换或可相互比较(例如，使用TypeConverter或类似设备)，以便LINQ查询可以对其进行比较?我在SO上也看到了其他类似的问题，但没有任何东西指向使类型之间可以转换以解决问题.

Given two lists of different types, is it possible to make those types convertible between or comparable to each other (eg with a TypeConverter or similar) so that a LINQ query can compare them? I've seen other similar questions on SO but nothing that points to making the types convertible between each other to solve the problem.

集合类型:

public class Data
{
    public int ID { get; set; }
}

public class ViewModel
{
    private Data _data;

    public ViewModel(Data data)
    {
        _data = data;
    }
}

所需用法:

    public void DoMerge(ObservableCollection<ViewModel> destination, IEnumerable<Data> data)
    {
        // 1. Find items in data that don't already exist in destination
        var newData = destination.Except(data);

        // ...
    }

这似乎是合乎逻辑的，因为我知道如何将ViewModel的实例与Data的实例进行比较，所以我应该能够提供一些比较逻辑，然后LINQ会将其用于.Except()之类的查询.这可能吗?

It would seem logical that since I know how to compare an instance of ViewModel to an instance of Data I should be able to provide some comparison logic that LINQ would then use for queries like .Except(). Is this possible?

推荐答案

您最好的选择是提供从Data到ViewModel的投影，以便您可以说

Your best bet is to provide a projection from Data to ViewModel so that you can say

var newData = destination.Except(data.Select(x => f(x)));

其中，f将Data映射到ViewModel.您还将需要IEqualityComparer<Data>.

where f maps Data to ViewModel. You will need a IEqualityComparer<Data> too.

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