c# - System.Text.Json 将字典序列化为数组

Question

是否可以使用 System.Text.Json 将字典序列化(和反序列化)为数组？

而不是 { "hello": "world" }我需要将我的字典序列化为 { "key": "hello", "value": "world" }最好不必在我的类的字典属性上设置属性。

使用 newtonsoft.json 可以这样:

class DictionaryAsArrayResolver : DefaultContractResolver
{
    protected override JsonContract CreateContract(Type objectType)
    {
        if (objectType.GetInterfaces().Any(i => i == typeof(IDictionary) || 
           (i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IDictionary<,>))))
        {
            return base.CreateArrayContract(objectType);
        }

        return base.CreateContract(objectType);
    }
}

Answer 1

您可以使用 JsonConverterFactory 来执行此操作制造特定的 JsonConverter<T> 对于要序列化为数组的每种字典类型。这是一个适用于所有实现 IDictionary<TKey, TValue> 的类的转换器。 :

public class DictionaryConverterFactory : JsonConverterFactory
{
    public override bool CanConvert(Type typeToConvert)
    {
        return typeToConvert.IsClass && typeToConvert.GetDictionaryKeyValueType() != null && typeToConvert.GetConstructor(Type.EmptyTypes) != null;
    }

    public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
    {
        var keyValueTypes = typeToConvert.GetDictionaryKeyValueType();
        var converterType = typeof(DictionaryAsArrayConverter<,,>).MakeGenericType(typeToConvert, keyValueTypes.Value.Key, keyValueTypes.Value.Value);
        return (JsonConverter)Activator.CreateInstance(converterType);
    }
}

public class DictionaryAsArrayConverter<TKey, TValue> : DictionaryAsArrayConverter<Dictionary<TKey, TValue>, TKey, TValue>
{
}

public class DictionaryAsArrayConverter<TDictionary, TKey, TValue> : JsonConverter<TDictionary> where TDictionary : class, IDictionary<TKey, TValue>, new()
{
    struct KeyValueDTO
    {
        public TKey Key { get; set; }
        public TValue Value { get; set; }
    }

    public override TDictionary Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        var list = JsonSerializer.Deserialize<List<KeyValueDTO>>(ref reader, options);
        if (list == null)
            return null;
        var dictionary = typeToConvert == typeof(Dictionary<TKey, TValue>) ? (TDictionary)(object)new Dictionary<TKey, TValue>(list.Count) : new TDictionary();
        foreach (var pair in list)
            dictionary.Add(pair.Key, pair.Value);
        return dictionary;
    }

    public override void Write(Utf8JsonWriter writer, TDictionary value, JsonSerializerOptions options)
    {
        JsonSerializer.Serialize(writer, value.Select(p => new KeyValueDTO { Key = p.Key, Value = p.Value }), options);
    }
}

public static class TypeExtensions
{
    public static IEnumerable<Type> GetInterfacesAndSelf(this Type type)
    {
        if (type == null)
            throw new ArgumentNullException();
        if (type.IsInterface)
            return new[] { type }.Concat(type.GetInterfaces());
        else
            return type.GetInterfaces();
    }

    public static KeyValuePair<Type, Type>? GetDictionaryKeyValueType(this Type type)
    {
        KeyValuePair<Type, Type>? types = null;
        foreach (var pair in type.GetDictionaryKeyValueTypes())
        {
            if (types == null)
                types = pair;
            else
                return null;
        }
        return types;
    }

    public static IEnumerable<KeyValuePair<Type, Type>> GetDictionaryKeyValueTypes(this Type type)
    {
        foreach (Type intType in type.GetInterfacesAndSelf())
        {
            if (intType.IsGenericType
                && intType.GetGenericTypeDefinition() == typeof(IDictionary<,>))
            {
                var args = intType.GetGenericArguments();
                if (args.Length == 2)
                    yield return new KeyValuePair<Type, Type>(args[0], args[1]);
            }
        }
    }
}

然后加工厂到 JsonSerializerOptions.Converters 本地如下:

var options = new JsonSerializerOptions
{
    Converters = { new DictionaryConverterFactory() },
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
};

var json = JsonSerializer.Serialize(dictionary, options);

var dictionary2 = JsonSerializer.Deserialize<TDictionary>(json, options);

或全局在 ASP.NET Core 中，如 How to set json serializer settings in asp.net core 3? 所示:

services.AddControllers().AddJsonOptions(options =>
{
    options.JsonSerializerOptions.Converters.Add(new DictionaryConverterFactory());
    options.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
});

底层个体转换器 DictionaryAsArrayConverter<TKey, TValue>如果您只想将某些字典类型序列化为数组，也可以直接使用。

笔记:

JsonSerializer目前不尊重 PropertyNamingPolicy 序列化时 KeyValuePair<TKey, TValue> (见 Issue #1197 )所以我不得不介绍一个 KeyValueDTO获取外壳"key"和 "value"根据您的问题的要求。

我没有为非通用 IDictionary 实现转换器类型。这可以作为答案的扩展来完成。

有关转换器工厂模式的更多信息，请参阅 How to write custom converters for JSON serialization in .NET : Sample factory pattern converter

等同于 DefaultContractResolver 的类型在 System.Text.Json -- JsonClassInfo 和 JsonPropertyInfo -- 是 内部 .有一个开放的增强 Equivalent of DefaultContractResolver in System.Text.Json #42001要求公共(public)等价物。

演示 fiddle here .