使用自定义的IEqualityComparer使用LINQ相交 [英] Intersect with a custom IEqualityComparer using Linq

问题描述

长话短说：我有对象的2集合。其中包括良好的价值观（让我们称之为好），其他默认值（先生默认）。我想联盟的相交好和默认和默认之间。换句话说：相交（联盟（好，默认值），默认值）。有人可能会认为它解析为默认设置，但这里是它得到棘手。我使用自定义的IEqualityComparer

Long story short: I have 2 collections of objects. One contains good values (Let's call it "Good"), the other default values (Mr. "Default"). I want the Intersect of the Union between Good and Default, and Default. In other words: Intersect(Union(Good, Default), Default). One might think it resolves as Default, but here is where it gets tricky : I use a custom IEqualityComparer.

我得到了以下的类：

class MyClass
{
    public string MyString1;
    public string MyString2;
    public string MyString3;
}

class MyEqualityComparer : IEqualityComparer<MyClass>
{
    public bool Equals(MyClass item1, MyClass item2)
    {
        if(item1 == null && item2 == null)
            return true;
        else if((item1 != null && item2 == null) ||
                (item1 == null && item2 != null))
            return false;

        return item1.MyString1.Equals(item2.MyString1) &&
               item1.MyString2.Equals(item2.MyString2);
    }

    public int GetHashCode(MyClass item)
    {
        return new { item.MyString1, item.MyString2 }.GetHashCode();
    }
}

下面是我收集好，并默认集合的特征

Here are the characteristic of my collections Good and Default collections :

默认：这是一个大组，包含所有想要{MyString1，MyString2}对，但MyString3值，你可以猜到，默认值

Default : It's a large set, containing all the wanted { MyString1, MyString2 } pairs, but the MyString3 values are, as you can guess, default values.

好：这是一个小集，主要包含这是在默认设置的项目，但也有一些很好的MyString3值。它也有一些{MyString1，MyString2}是想要的设置之外

Good : It's a smaller set, containing mostly items which are in the Default set, but with some good MyString3 values. It also has some { MyString1, MyString2 } that are outside of the wanted set.

我想要做的是：仅是在默认的从优秀项目，但在默认情况下添加其他项目到

What I want to do is this : Take only the items from Good that are in Default, but add the other items in Default to that.

在这里，我的想法是，我最好的尝试：

Here is, what I think is, my best try :

HalfWantedResult = Good.Union(Default, new MyEqualityComparer());
WantedResult= HalfWantedResult.Intersect(Good, new MyEqualityComparer());

我教它应该有工作，但结果我得到的是基本上只有好{MyString1，MyString2 }对设定，但是所有从默认设置来了，所以我全部横跨具有默认值。我也试过切换默认和最后相交的好，但我得到了相同的结果。

I taught it should have worked, but the result I get is basically only the good { MyString1, MyString2 } pairs set, but all coming from the Default set, so I have the default value all across. I also tried switching the Default and Good of the last Intersect, but I get the same result.

推荐答案

这一切首先是错误：

public bool Equals(MyClass item1, MyClass item2)
{
    return GetHashCode(item1) == GetHashCode(item2);
}

如果的哈希码的是肯定的相应的2项是不同的，但如果不同它们相等不能保证相应的2项是相等的。

If the hashcode's are different for sure the corresponding 2 items are different, but if they're equal is not guaranteed that the corresponding 2 items are equal.

因此，这是正确的等于实施

public bool Equals(MyClass item1, MyClass item2)
{
    if(object.ReferenceEquals(item1, item2))
        return true;
    if(item1 == null || item2 == null)
        return false;
    return item1.MyString1.Equals(item2.MyString1) &&
           item1.MyString2.Equals(item2.MyString2);
}

作为的西裤建议（期待我）的代码如下：

As Slacks suggested (anticipating me) the code is the following:

var Default = new List<MyClass>
{
    new MyClass{MyString1="A",MyString2="A",MyString3="-"},
    new MyClass{MyString1="B",MyString2="B",MyString3="-"},
    new MyClass{MyString1="X",MyString2="X",MyString3="-"},
    new MyClass{MyString1="Y",MyString2="Y",MyString3="-"},
    new MyClass{MyString1="Z",MyString2="Z",MyString3="-"},

};
var Good = new List<MyClass>
{
    new MyClass{MyString1="A",MyString2="A",MyString3="+"},
    new MyClass{MyString1="B",MyString2="B",MyString3="+"},
    new MyClass{MyString1="C",MyString2="C",MyString3="+"},
    new MyClass{MyString1="D",MyString2="D",MyString3="+"},
    new MyClass{MyString1="E",MyString2="E",MyString3="+"},
};
var wantedResult = Good.Intersect(Default, new MyEqualityComparer())
                       .Union(Default, new MyEqualityComparer());

// wantedResult:
// A A +
// B B +
// X X -
// Y Y -
// Z Z -

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