C# 当属性类型包括泛型类型时，如何将泛型JsonConverter应用于泛型类的属性？

我对Json.NET有一个问题。当属性类型包括类本身的泛型类型参数时，我需要为一个泛型类中的不同属性使用不同的泛型JSONConverter

让我们使用以下泛型类，其中一些需要转换的属性使用参数

TTable

：

public class ExpresssionDTO<TTable> : BaseDTO where TTable : class
{
    [JsonProperty(ItemConverterType = typeof(PredicateSerializationConverter<>))]
    public ICollection<Expression<Func<TTable, bool>>> Predicates { get; set; } = new List<Expression<Func<TTable, bool>>>();

    [JsonConverter(converterType: typeof(FilterSerializationConverter<>))]
    public Expression<Func<TTable, object>> Filter { get; set; } = null;
}

对于

DefaultContractResolver

，也会出现此问题

---

有什么方法可以解决我的问题吗？

您要做的是使用泛型参数

TTable

作为自定义JSON转换器的泛型参数，如下所示：

public class ExpresssionDTO<TTable> : BaseDTO where TTable : class
{
    [JsonProperty(ItemConverterType = typeof(PredicateSerializationConverter<TTable>))] // Here
    public ICollection<Expression<Func<TTable, bool>>> Predicates { get; set; } = new List<Expression<Func<TTable, bool>>>();

    [JsonConverter(converterType: typeof(FilterSerializationConverter<TTable>))] // And here
    public Expression<Func<TTable, object>> Filter { get; set; } = null;
}

然后将其应用于模型，如下所示，将打开的泛型转换器类型作为转换器参数传递：

public class ExpresssionDTO<TTable> : BaseDTO where TTable : class
{
    [JsonProperty(ItemConverterType = typeof(GenericFuncExpressionArgumentConverterDecorator), ItemConverterParameters = new object [] { typeof(PredicateSerializationConverter<>) })]
    public ICollection<Expression<Func<TTable, bool>>> Predicates { get; set; } = new List<Expression<Func<TTable, bool>>>();

    [JsonConverter(typeof(GenericFuncExpressionArgumentConverterDecorator), new object [] { typeof(FilterSerializationConverter<>) })]
    public Expression<Func<TTable, object>> Filter { get; set; } = null;
}

public class expressiondto:BaseDTO其中TTable:class
{
[JsonProperty（ItemConverterType=typeof（GenericFunctionExpressionArgumentConverterDecorator），ItemConverterParameters=new object[]{typeof（PredicateSerializationConverter）}]
公共ICollection谓词{get；set；}=new List（）；
[JsonConverter（typeof（GenericFunctionExpressionArgumentConverterDecorator），新对象[]{typeof（FilterSerializationConverter）}]
公共表达式筛选器{get；set；}=null；
}

---

演示小提琴。

将属性的类型放入空的

@Charlieface中，该属性也不起作用-如果我尝试将泛型类型传递到括号中，则会出现编译器时间错误。

PredicateSerializationConverter

这会产生什么错误？@Charlieface编译器时间错误您不能在属性中使用泛型参数，请参阅。实际类型作为参数传递给and

WriteJson（）

，因此您需要使转换器非通用，并通过其中的反射完成所有操作。或者，您可以使用自定义契约解析器应用转换器。你能和我共用一个房间吗？

public class ExpresssionDTO<TTable> : BaseDTO where TTable : class
{
    [JsonProperty(ItemConverterType = typeof(PredicateSerializationConverter<TTable>))] // Here
    public ICollection<Expression<Func<TTable, bool>>> Predicates { get; set; } = new List<Expression<Func<TTable, bool>>>();

    [JsonConverter(converterType: typeof(FilterSerializationConverter<TTable>))] // And here
    public Expression<Func<TTable, object>> Filter { get; set; } = null;
}

public class GenericFuncExpressionArgumentConverterDecorator : JsonConverter
{
    readonly Type openGenericConverterType;
    volatile Tuple<Type, JsonConverter> converterCache;
            
    public GenericFuncExpressionArgumentConverterDecorator(Type openGenericConverterType)
    {
        if (openGenericConverterType == null)
            throw new ArgumentNullException();
        if (!openGenericConverterType.IsSubclassOf(typeof(JsonConverter)))
            throw new ArgumentException(string.Format("{0} is not a JsonConvreter", GetType().Name));
        if (!openGenericConverterType.IsGenericTypeDefinition)
            throw new ArgumentException(string.Format("{0} is not an open generic type", GetType().Name));
        this.openGenericConverterType = openGenericConverterType;
    }

    public override bool CanConvert(Type objectType) => 
        throw new NotImplementedException(string.Format("{0} is intended to be applied via a JsonConverter or JsonProperty attribute", GetType().Name));

    JsonConverter GetConverter(Type objectType)
    {
        var cache = converterCache;
        if (cache != null && cache.Item1 == objectType)
            return cache.Item2;
        // Despite the documentation, Expression<T> is not actually sealed in .Net 5!
        // https://github.com/dotnet/runtime/blob/master/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/LambdaExpression.cs#L174
        var expressionType = objectType.BaseTypesAndSelf().Where(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Expression<>)).FirstOrDefault();
        if (expressionType == null)
            throw new JsonSerializationException(string.Format("Invalid expression type {0}", objectType));
        var delegateType = objectType.GetGenericArguments().Single();
        if (!delegateType.IsGenericType || delegateType.GetGenericTypeDefinition() != typeof(Func<,>))
            throw new JsonSerializationException(string.Format("Invalid delegate type {0}", delegateType));
        var argType = delegateType.GetGenericArguments()[0];
        var converterType = openGenericConverterType.MakeGenericType(new [] { argType });
        var converter = (JsonConverter)Activator.CreateInstance(converterType);
        converterCache = Tuple.Create(objectType, converter);
        return converter;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) =>
        GetConverter(objectType).ReadJson(reader, objectType, existingValue, serializer);

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) =>
        GetConverter(value.GetType()).WriteJson(writer, value, serializer);
}

public static class TypeExtensions
{
    public static IEnumerable<Type> BaseTypesAndSelf(this Type type)
    {
        while (type != null)
        {
            yield return type;
            type = type.BaseType;
        }
    }
}

public class ExpresssionDTO<TTable> : BaseDTO where TTable : class
{
    [JsonProperty(ItemConverterType = typeof(GenericFuncExpressionArgumentConverterDecorator), ItemConverterParameters = new object [] { typeof(PredicateSerializationConverter<>) })]
    public ICollection<Expression<Func<TTable, bool>>> Predicates { get; set; } = new List<Expression<Func<TTable, bool>>>();

    [JsonConverter(typeof(GenericFuncExpressionArgumentConverterDecorator), new object [] { typeof(FilterSerializationConverter<>) })]
    public Expression<Func<TTable, object>> Filter { get; set; } = null;
}