Linq查询以查找嵌套列表包含序列的匹配项[重复]

Question

鉴于这两个对象：

public class Foo{
   public string Result {get;set;}
   public List<Bar> Bars {get;set;}
}

public class Bar{
   public string Left {get;set;}
   public string Right {get;set;}
}

这些实例如下所示：

List<Foo> myFoos = new List<Foo>()
        {
    new Foo { Bars = new List<Bar>
        {
            new Bar { Left = "myLeft1", Right = "myValue1"},
            new Bar { Left = "myLeft2", Right = "myValue2"}
        },
        Result = "TheWinningResult"},
    new Foo { Bars = new List<Bar>
        {
            new Bar { Left = "myLeft2", Right = "myValue2"},
            new Bar { Left = "myLeft3", Right = "myValue3"}
        },
        Result = "TheLosingResult"},
    new Foo{ Bars = new List<Bar>
        {
            new Bar { Left = "myLeft1", Right = "myValue1"},
            new Bar { Left = "myLeft2", Right = "myValue2"},
            new Bar { Left = "myLeft3", Right = "myValue3"}
        },
        Result = "TheOtherLosingResult"},
};

List<Bar> bars = new List<Bar>()
{
     new Bar{  Left = "myLeft1", Right = "myValue1" },
     new Bar{  Left = "myLeft2", Right = "myValue2" }
};

我正在尝试查找 FirstOrDefault() Foo 其中 Foo.Bars 与 bars 完全匹配

在这种情况下，我试图返回Foo，而Result 是“TheWinningResult”

我尝试了以下方法：

Foo foo =  myFoos.Where(t => t.Bars.All(t2 => bars.Contains(t2))).FirstOrDefault();

Foo foo = myFoos.Where(t => bars.All(r => t.Bars.Contains(r))).FirstOrDefault();     

Foo foo =   myFoos.FirstOrDefault(t => t.Bars.Any(r => bars.All(ru => ru.Left == r.Left && ru.Right == r.Right)));

知道我哪里出错了吗？

更新

我忘了说，Foo 中的Bars 的顺序应该不重要。

Answer 1

问题在于 contains 如何比较对象。默认情况下，比较是通过引用相等来完成的。在这里，您需要不同的行为 - 按内容比较平等。这样做覆盖Equals 和GetHashCode 的Bar：

public override bool Equals(object obj)
{
    var other = obj as Bar;
    if (obj == null)
        return false;
    return other.Left == Left && other.Right == Right;
}

public override int GetHashCode()
{
    unchecked
    {
        int hash = 17;
        hash = hash * 23 + Left.GetHashCode();
        hash = hash * 23 + Right.GetHashCode();
        return hash;
    }
}

然后可以通过以下方式检索正确的对象：

var result = myFoos.Where(item => bars.Count == item.Bars.Count && 
                                  !bars.Except(item.Bars).Any());

或者如果使用SequenceEqual:

var result = myFoos.Where(item => bars.SequenceEqual(item.Bars));

---

另一种方法是实现IEqualityComparer<Bar> 并调用匹配的Contains 重载：

var result = myFoos.Where(t => t.Bars.All(t2 => bars.Contains(t2, new BarEqualityComparer())));

---

至于您的第三次尝试，问题在于 All 和 Any 是相反的：您希望 foo 中的所有条都与 bars 列表中的任何项目匹配：

Foo foo = myFoos.FirstOrDefault(t => t.Bars.All(r => bars.Any(ru => ru.Left == r.Left && ru.Right == r.Right)));

---

对于 GetHashCode 的覆盖是什么，您可以阅读以下两个：

1. Object.GetHashCode
2. Why is it important to override GetHashCode when Equals method is overridden?