Question

对于使用HashSet的自定义比较器，我必须有一些误解。我收集了很多不同类型的数据，我作为Json中间存储。为了对它进行操作，我使用的是Json.NET，特别是JObject，JArray和Jtoken。

通常我会在收集时为这些内容添加一些内联元素，并以＆＃34; tbp _＆＃34;为前缀。我需要知道在（或不是）之前是否收集了表示为JObject的特定数据。为了做到这一点，我有一个自定义IEqualityComparer，它扩展了Json.NET提供的实现。它在使用提供的实现检查值相等之前去掉元数据：

public class EntryComparer : JTokenEqualityComparer
{
    private static string _excludedPrefix = "tbp_";

    public JObject CloneForComparison(JObject obj)
    {
        var clone = obj.DeepClone() as JObject;
        var propertiesToRemove = clone
            .Properties()
            .Where(p => p.Name.StartsWith(_excludedPrefix));

        foreach (var property in propertiesToRemove)
        {
            property.Remove();
        }

        return clone;
    }

    public bool Equals(JObject obj1, JObject obj2)
    {
        return base.Equals(CloneForComparison(obj1), CloneForComparison(obj2));
    }

    public int GetHashCode(JObject obj)
    {
        return base.GetHashCode(CloneForComparison(obj));
    }
}

我使用HashSet来跟踪我正在操作的数据，因为我只需要知道它是否已经存在。我使用EntryComparer的实例初始化HashSet。我的测试是：

public class EntryComparerTests
{
    EntryComparer comparer;
    JObject j1;
    JObject j2;

    public EntryComparerTests()
    {
        comparer = new EntryComparer();
        j1 = JObject.Parse(@"
        {
          'tbp_entry_date': '2017-03-25T21:25:53.127993-04:00',
          'from_date': '1/6/2017',
          'to_date': '2/7/2017',
          'use': '324320',
          'reading': 'act',
          'kvars': '0.00',
          'demand': '699.10',
          'bill_amt': '$28,750.75'
        }");
        j2 = JObject.Parse(@"
        {
          'tbp_entry_date': '2017-03-10T18:59:00.537745-05:00',
          'from_date': '1/6/2017',
          'to_date': '2/7/2017',
          'use': '324320',
          'reading': 'act',
          'kvars': '0.00',
          'demand': '699.10',
          'bill_amt': '$28,750.75'
        }");
    }

    [Fact]
    public void Test_Equality_Comparer_GetHashCode()
    {  
        Assert.Equal(comparer.GetHashCode(j1), comparer.GetHashCode(j2));
        Assert.Equal(true, comparer.Equals(j1, j2));
    }

    [Fact]
    public void Test_Equality_Comparer_Hashset_Contains()
    {
        var hs = new HashSet<JObject>(comparer);
        hs.Add(j1);

        Assert.Equal(true, hs.Contains(j2));
    }
}

Test_Equality_Comparer_GetHashCode()次，但Test_Equality_Comparer_Hashset_Contains()失败。 j1和j2应该被视为平等，并且根据第一次测试的结果，我在这里缺少什么？

Answer 1

更改班级的签名：

public class EntryComparer : JTokenEqualityComparer, IEqualityComparer<JObject>

否则使用的GetHashCode()和Equals()是基类中的那些（具有不同的“签名”......基类实现IEqualityComparer<JToken>，这是因为HashSet<>）不会调用您的方法。

然后删除属性有一个小错误：

var propertiesToRemove = clone
    .Properties()
    .Where(p => p.Name.StartsWith(_excludedPrefix))
    .ToArray();

最好是“隐藏”JTokenEqualityComparer并将其设为私有字段，例如：

public class EntryComparer : IEqualityComparer<JObject>
{
    private static readonly JTokenEqualityComparer _comparer = new JTokenEqualityComparer();
    private static readonly string _excludedPrefix = "tbp_";

    public static JObject CloneForComparison(JObject obj)
    {
        var clone = obj.DeepClone() as JObject;
        var propertiesToRemove = clone
            .Properties()
            .Where(p => p.Name.StartsWith(_excludedPrefix))
            .ToArray();

        foreach (var property in propertiesToRemove)
        {
            property.Remove();
        }

        return clone;
    }

    public bool Equals(JObject obj1, JObject obj2)
    {
        return _comparer.Equals(CloneForComparison(obj1), CloneForComparison(obj2));
    }

    public int GetHashCode(JObject obj)
    {
        return _comparer.GetHashCode(CloneForComparison(obj));
    }
}

HashSet.Contains和自定义IEqualityComparer的意外结果

1 个答案: