Intro
今天在项目里遇到一个需求，大概是这样的我要比较两个 JSON 字符串是不是相等，JSON 字符串其实是一个 Dictionary<string, string> 但是顺序可能不同，和上一篇 record 使用场景 中的第一个需求类似，前面我们介绍过使用 record 可以比较方便的解决，但是我们的项目是 .netcoreapp3.1 的，不能使用 record，如何比较方便的比较呢？我们能否自己实现一个类似于 record 的类型，基于值去比较呢？于是就有了本文的探索
StringValueDictioanry
实现了一个基于值进行比较的字典，实现代码如下，实现的比较简单，涉及到一些简单的知识点，平时不怎么用已经忘了怎么写了，通过写下面的代码又学习了一下
先来看测试代码吧，测试代码如下：
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[Fact]public void EqualsTest(){ var abc = new { Id = 1, Name = "Tom" }; var dic1 = StringValueDictionary.FromObject(abc); var dic2 = StringValueDictionary.FromObject(new Dictionary<string, object>() { {"Name", "Tom" }, {"Id", 1}, }); Assert.True(dic1 == dic2); Assert.Equal(dic1, dic2);}[Fact]public void DistinctTest(){ var abc = new { Id = 1, Name = "Tom" }; var dic1 = StringValueDictionary.FromObject(abc); var dic2 = StringValueDictionary.FromObject(new Dictionary<string, object>() { {"Id", 1}, {"Name", "Tom" }, }); var set = new HashSet<StringValueDictionary>(); set.Add(dic1); set.Add(dic2); Assert.Single(set);}[Fact]public void CloneTest(){ var dic1 = StringValueDictionary.FromObject(new Dictionary<string, object>() { {"Id", 1}, {"Name", "Tom" } }); var dic2 = dic1.Clone(); Assert.False(ReferenceEquals(dic1, dic2)); Assert.True(dic1 == dic2);}[Fact]public void ImplicitConvertTest(){ var abc = new { Id = 1, Name = "Tom" }; var stringValueDictionary = StringValueDictionary.FromObject(abc); Dictionary<string, string> dictionary = stringValueDictionary; Assert.Equal(stringValueDictionary.Count, dictionary.Count); var dic2 = StringValueDictionary.FromObject(dictionary); Assert.Equal(dic2, stringValueDictionary); Assert.True(dic2 == stringValueDictionary);} |
从上面的代码可能大概能看出一些实现，重写了默认的 Equals 和 GetHashCode，并重载了“==” 运算符，并且实现了一个从 StringValueDictionary 到 Dictionary 的隐式转换，来看下面的实现代码：
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public sealed class StringValueDictionary : IEquatable<StringValueDictionary>{ private readonly Dictionary<string, string?> _dictionary = new(); private StringValueDictionary(IDictionary<string, string?> dictionary) { foreach (var pair in dictionary) { _dictionary[pair.Key] = pair.Value; } } private StringValueDictionary(StringValueDictionary dictionary) { foreach (var key in dictionary.Keys) { _dictionary[key] = dictionary[key]; } } public static StringValueDictionary FromObject(object obj) { if (obj is null) throw new ArgumentNullException(nameof(obj)); if (obj is IDictionary<string, string?> dictionary) { return new StringValueDictionary(dictionary); } if (obj is IDictionary<string, object?> dictionary2) { return new StringValueDictionary(dictionary2.ToDictionary(p => p.Key, p => p.Value?.ToString())); } if (obj is StringValueDictionary dictionary3) { return new StringValueDictionary(dictionary3); } return new StringValueDictionary(obj.GetType().GetProperties() .ToDictionary(p => p.Name, p => p.GetValue(obj)?.ToString())); } public static StringValueDictionary FromJson(string json) { Guard.NotNull(json, nameof(json)); var dic = json.JsonToObject<Dictionary<string, object?>>() .ToDictionary(x => x.Key, x => x.Value?.ToString()); return new StringValueDictionary(dic); } public StringValueDictionary Clone() => new(this); public int Count => _dictionary.Count; public bool ContainsKey(string key) => _dictionary.ContainsKey(key) ? _dictionary.ContainsKey(key) : throw new ArgumentOutOfRangeException(nameof(key)); public string? this[string key] => _dictionary[key]; public Dictionary<string, string>.KeyCollection Keys => _dictionary.Keys!; public bool Equals(StringValueDictionary? other) { if (other is null) return false; if (other.Count != Count) return false; foreach (var key in _dictionary.Keys) { if (!other.ContainsKey(key)) { return false; } if (_dictionary[key] != other[key]) { return false; } } return true; } public override bool Equals(object obj) { return Equals(obj as StringValueDictionary); } public override int GetHashCode() { var stringBuilder = new StringBuilder(); foreach (var pair in _dictionary) { stringBuilder.Append($"{pair.Key}={pair.Value}_"); } return stringBuilder.ToString().GetHashCode(); } public static bool operator ==(StringValueDictionary? current, StringValueDictionary? other) { return current?.Equals(other) == true; } public static bool operator !=(StringValueDictionary? current, StringValueDictionary? other) { return current?.Equals(other) != true; } public static implicit operator Dictionary<string, string?>(StringValueDictionary dictionary) { return dictionary._dictionary; }} |
More
上述代码实现的有点粗糙，可能会有一些问题，仅供参考
以上代码基本实现了基于想要的值的相等性比较以及 Clone（复制、克隆）的目标
实现相等性比较的时候，
Equals和GetHashCode方法也要重写，如果没有重写GetHashCode，编译器也会给出警告，如果没有重写GetHashCode在实际在HashSet或者Dictionary里可能会出现重复key重载运算符的时候需要一个静态方法，"==" 和 "!=" 是一对操作运算符，如果要实现两个都要实现，不能只实现其中一个
implicit 也算是一个特殊的运算符，巧妙的使用隐式转换可以大大简化代码的写法，
StackExchange.Redis中就使用了implicit来实现RedisValue和string等其他常用类型的隐式转换
References
https://github.com/WeihanLi/WeihanLi.Common/blob/dev/src/WeihanLi.Common/Models/StringValueDictionary.cs
https://github.com/WeihanLi/WeihanLi.Common/blob/dev/test/WeihanLi.Common.Test/ModelsTest/StringValueDictionaryTest.cs
以上就是C# 如何实现一个基于值相等性比较的字典的详细内容，更多关于c# 实现值相等性比较的字典的资料请关注服务器之家其它相关文章！
原文链接：https://www.cnblogs.com/weihanli/p/14352741.html
