使Json.NET不兼容$ type [英] make Json.NET ignore $type if it's incompatible

问题描述

我有一个IReadOnlyList<RoadLaneDto>类型的属性.为了与其他地方兼容，我将其更改为RoadLaneDto[].现在，当我反序列化旧数据时，会出现以下错误:

I had a property of type IReadOnlyList<RoadLaneDto>. To be compatible elsewhere, I changed it to RoadLaneDto[]. Now, when I deserialize my old data, I get this error:

Newtonsoft.Json.JsonSerializationException:在JSON'System.Collections.Generic.List`1 [[Asi.Shared.Interfaces.DTOs.Map.RoadLaneDto，Asi.Shared.Interfaces，Version = 1.0.0.0，文化中指定的类型= neutral，PublicKeyToken = null]]，mscorlib，Version = 4.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089'与'Asi.Shared.Interfaces.DTOs.Map.RoadLaneDto []，Asi.Shared.Interfaces，版本= 1.0.0.0，文化=中性，PublicKeyToken =空".路径"Shapes [0] .Lanes.$ type"，第78行，位置132.

Newtonsoft.Json.JsonSerializationException : Type specified in JSON 'System.Collections.Generic.List`1[[Asi.Shared.Interfaces.DTOs.Map.RoadLaneDto, Asi.Shared.Interfaces, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]], mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' is not compatible with 'Asi.Shared.Interfaces.DTOs.Map.RoadLaneDto[], Asi.Shared.Interfaces, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Path 'Shapes[0].Lanes.$type', line 78, position 132.

什么是使它们兼容的正确方法?我可以提出$type的建议而不是要求吗?我可以编写某种自定义转换器来处理这种情况吗?

What is the right approach to make these compatible? Can I make the $type a suggestion rather than a requirement? Can I write a custom converter of some kind that would handle this situation?

推荐答案

通常，出于以下原因，我不建议序列化集合类型:您想自由更改集合的类型(尽管不一定要更改类型)集合 item )而没有序列化问题.如果要使用与Json.NET的默认值不同的特定集合类型来实现集合接口值属性，例如将HashSet<T>表示为ICollection<T>，则可以在包含类的默认构造函数中分配它，并且Json.NET将使用预分配的集合.要仅序列化对象类型而不序列化集合类型，请设置 TypeNameHandling = TypeNameHandling.Objects .

In general I don't recommend serializing collection types, for precisely this reason: you want to be free to change the type of collection (though not necessarily the type of collection item) without serialization problems. If you want to implement a collection-interface-valued property with a specific collection type that differs from Json.NET's defaults, say a HashSet<T> for an ICollection<T>, you can allocate it in the default constructor of the containing class, and Json.NET will use the pre-allocated collection. To serialize only object types and not collection types, set TypeNameHandling = TypeNameHandling.Objects.

话虽如此，以下转换器在反序列化第1级数组时将吞下类型信息.

That being said, the following converter will swallow type information when deserializing an array of rank 1:

public class IgnoreArrayTypeConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType.IsArray && objectType.GetArrayRank() == 1 && objectType.HasElementType;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (!CanConvert(objectType))
            throw new JsonSerializationException(string.Format("Invalid type \"{0}\"", objectType));
        if (reader.TokenType == JsonToken.Null)
            return null;
        var token = JToken.Load(reader);
        var itemType = objectType.GetElementType();
        return ToArray(token, itemType, serializer);
    }

    private static object ToArray(JToken token, Type itemType, JsonSerializer serializer)
    {
        if (token == null || token.Type == JTokenType.Null)
            return null;
        else if (token.Type == JTokenType.Array)
        {
            var listType = typeof(List<>).MakeGenericType(itemType);
            var list = (ICollection)token.ToObject(listType, serializer);
            var array = Array.CreateInstance(itemType, list.Count);
            list.CopyTo(array, 0);
            return array;
        }
        else if (token.Type == JTokenType.Object)
        {
            var values = token["$values"];
            if (values == null)
                return null;
            return ToArray(values, itemType, serializer);
        }
        else
        {
            throw new JsonSerializationException("Unknown token type: " + token.ToString());
        }
    }

    public override bool CanWrite { get { return false; } }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

然后您可以像使用它一样

Then you can use it like:

public class RootObject
{
    [JsonProperty(TypeNameHandling = TypeNameHandling.None)] // Do not emit array type information
    [JsonConverter(typeof(IgnoreArrayTypeConverter))]        // Swallow legacy type information
    public string[] Lanes { get; set; }
}

或者，您可以在设置中全局使用转换器，并使其包含所有阵列的类型信息:

Or, you can use the converter globally in settings and have it swallow type information for all arrays:

    var settings = new JsonSerializerSettings { Converters = new JsonConverter[] { new IgnoreArrayTypeConverter() }, TypeNameHandling = TypeNameHandling.All };

Json.NET确实支持多维数组，因此可以将支持扩展到等级大于1的数组.

Json.NET does support multidimensional arrays so extending support to arrays of rank > 1 would be possible.

这篇关于使Json.NET不兼容$ type的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！