Csharp 确定System.Text.Json序列化中是否无法识别Type

在构造已声明类型的约定时，我不知道有什么方法可以使实际类型被序列化.

但是，您可以强制System.Text.Json在序列化意外派生类型时自动引发异常.为此，您需要创建一个JsonTypeInfo modifier，以自动将所有相关非密封类型的JsonPolymorphismOptions.UnknownDerivedTypeHandling设置为FailSerialization:

public static partial class JsonExtensions
{
    public static Action<JsonTypeInfo> SetupUnknownDerivedTypeHandling(bool objectsOnly = false) =>
        (typeInfo) =>
    {
        // Polymorphism using type discriminators is only supported for type hierarchies that use the default converters for objects, collections, and dictionary types.
        if (typeInfo.Kind == JsonTypeInfoKind.None || typeInfo.Type.IsSealed || typeInfo.Type == typeof(object))
            return;
        if (objectsOnly && typeInfo.Kind != JsonTypeInfoKind.Object)
            return;
        // TODO: decide whether to fail serialization even for types marked with
        // [JsonPolymorphic(UnknownDerivedTypeHandling = FallBackToBaseType or FallBackToNearestAncestor)]
        if (typeInfo.PolymorphismOptions == null)
        {
            typeInfo.PolymorphismOptions = new() { DerivedTypes = { new(typeInfo.Type) } };
            // TODO: decide whether to fail serialization even for types marked with
            // [JsonPolymorphic(UnknownDerivedTypeHandling = FallBackToBaseType or FallBackToNearestAncestor)]
            // If so, move the setting of UnknownDerivedTypeHandling out of this if statement.
            typeInfo.PolymorphismOptions.UnknownDerivedTypeHandling = JsonUnknownDerivedTypeHandling.FailSerialization;
        };
    };
}

然后设置选项，例如，如下所示:

var options = new JsonSerializerOptions()
{
    // Configure either a DefaultJsonTypeInfoResolver or some JsonSerializerContext and add the required modifier:
    TypeInfoResolver = new DefaultJsonTypeInfoResolver() 
        .WithAddedModifier(JsonExtensions.SetupUnknownDerivedTypeHandling()),
    // Set other options as required.
};

备注:

• 因为System.Text.Json总是为声明为object的引用序列化完整的具体类型，所以在这种情况下我不会抛出异常.

• 多态类型可以为JsonPolymorphicAttribute.UnknownDerivedTypeHandling配置特定的行为，其中FailSerialization是默认行为.来自docs家的:

  JsonUnknownDerivedTypeHandling value	Effect
  FailSerialization	An object of undeclared runtime type will fail polymorphic serialization. The default.
  FallBackToBaseType	An object of undeclared runtime type will fall back to the serialization contract of the base type.
  FallBackToNearestAncestor	An object of undeclared runtime type will revert to the serialization contract of the nearest declared ancestor type. Certain interface hierarchies are not supported due to diamond ambiguity constraints.

  如果您的某些类型的静态配置行为不是FailSerialization，而您想要覆盖它，则可以通过将该设置移到if (typeInfo.PolymorphismOptions == null)判断之外来执行此操作.

• 就我个人而言，我不建议意外的集合或字典类型导致序列化失败.将属性声明为IList<T>或IDictionary<TKey,TValue>并使用某些具体类型实现属性是很常见的.如果通过objectsOnly = false，则在这种情况下将抛出异常.

演示小提琴here.