使用 JSON.NET 使用 IEnumerable 反序列化对象

Question

考虑以下 json 和模型：

{
    "Reference": "Bay House 22",
    "Appliances": [
        {
            "Reference": "Kitchen Appliance 1",
            "ApplianceType": "0",
            "NumberOfSlots": 4
        },
        {
            "Reference": "Kitchen Appliance 2",
            "ApplianceType": "1",
            "Capacity": 1500
        }
    ]
}

public class HouseModel
{
    public String Reference { get; set; }
    [JsonConverter(typeof(ApplianceModelConverter))]
    public IEnumerable<IApplianceModel> Appliances { get; set; }
}

public interface IApplianceModel
{
    String Reference { get; set; }
    ApplianceType ApplianceType { get; set; } // this is an enum
}

public class ToasterModel : IApplianceModel
{
    public String Reference { get; set; }
    public ApplianceType ApplianceType { get; set; }

    public Int32 NumberOfSlots { get; set; }
}

public class KettleModel : IApplianceModel
{
    public String Reference { get; set; }
    public ApplianceType ApplianceType { get; set; }

    public Int32 Capacity { get; set; }
}

我正在尝试使用自定义 json 转换器反序列化可能是 Toaster 或 Kettle 的 IEnumerable。这里的想法是，一旦我通过查看 json 知道 ApplianceType 是什么，我就可以 return 一个具体类型。我一直在关注 this Whosebug post 尝试让它工作，但没有成功。

这是转换器代码：

public abstract class JsonCreationConverter<T> : JsonConverter
{
    protected abstract T Create(Type objectType, JObject jObject);

    public override Boolean CanConvert(Type objectType)
    {
        return typeof(T).IsAssignableFrom(objectType);
    }

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

    public override Object ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
    {
        // Load JObject from stream
        JObject jObject = JObject.Load(reader);

        // Create target object based on JObject
        T target = Create(objectType, jObject);

        // Populate the object properties
        serializer.Populate(jObject.CreateReader(), target);

        return target;
    }
}

public class ApplianceModelConverter: JsonCreationConverter<IApplianceModel>
{
    protected override IApplianceModel Create(Type objectType, JObject jObject)
    {
        if (jObject["applianceType "] == null)
        {
            throw new ArgumentException("Missing ApplianceType");
        }

        ApplianceType applianceType = jObject.Value<ApplianceType>();

        switch (applianceType )
        {
            case ApplianceType.Kettle:
                return new KettleModel();
            case ApplianceType.Toaster: 
                return new ToasterModel();
            default:
                throw new InvalidEnumArgumentException("ApplianceType not supported");
        }
    }
}

目前我在执行此行时抛出异常：JObject jObject = JObject.Load(reader); in the JsonCreationConverter

Newtonsoft.Json.JsonReaderException: 'Error reading JObject from JsonReader. Current JsonReader item is not an object: StartArray. Path 'Appliances'

我猜它正在进入 IEnumerable 并且只是失败了，我在这里做错了什么？

Answer 1

注释这行代码

    public class HouseModel
{
    public String Reference { get; set; }
    //[JsonConverter(typeof(ApplianceModelConverter))] //=> You don't need this
    public IEnumerable<IApplianceModel> Appliances { get; set; }
}

也将 Create 方法更改为此

 protected override IApplianceModel Create(Type objectType, JObject jObject)
    {
        if (jObject["ApplianceType"] == null) //case sensitive
        {
            throw new ArgumentException("Missing ApplianceType");
        }

        //ApplianceType applianceType = jObject.Value<ApplianceType>(); //this might throw invalid cast exception
        ApplianceType applianceType = jObject["ApplianceType"].ToObject<ApplianceType>();


        switch (applianceType)
        {
            case ApplianceType.Kettle:
                return new KettleModel();
            case ApplianceType.Toaster:
                return new ToasterModel();
            default:
                throw new InvalidEnumArgumentException("ApplianceType not supported");
        }
    }

如果我们使用这个方法反序列化

string json = "{\"Reference\": \"Bay House 22\",\"Appliances\": [{\"Reference\": \"Kitchen Appliance 1\",\"ApplianceType\": \"0\",\"NumberOfSlots\": 4},{\"Reference\": \"Kitchen Appliance 2\",\"ApplianceType\": \"1\",\"Capacity\": 1500}]}";

HouseModel houseModels = JsonConvert.DeserializeObject<HouseModel>(json, new ApplianceModelConverter());

使用 JSON.NET 使用 IEnumerable 反序列化对象

Deserialize an object with an IEnumerable using JSON.NET

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