objects - serializar json c#

Deserializar una matriz JSON heterogénea en la Lista covariante<> utilizando JSON.NET

Question

Tengo una matriz JSON que contiene objetos de diferentes tipos con diferentes propiedades. Una de las propiedades se llama "tipo" y determina el tipo de elemento de la matriz. Aquí hay un ejemplo de mis datos:

   [{
        type : "comment",
        text : "xxxx"
    }, {
        type : "code",
        tokens : [{
                type : "ref",
                data : "m"
            }, {
                type : "operator",
                data : "e"
            }
        ]
    }, {
        type : "for",
        boundLocal : {
            type : "local",
            name : "i",
            kind : "Number"
        },
        upperBound : {
            type : "ref",
            tokens : [{
                    type : "operator",
                    data : "3"
                }, {
                    type : "operator",
                    data : "0"
                }
            ]
        },
        body : [{
                type : "code",
                tokens : [{
                        type : "ref",
                        data : "x"
                    }
                ]
            }, {
                type : "code",
                tokens : [{
                        type : "ref",
                        data : "y"
                    }
                }
                ]
        ]
    ]

Para asignar esos objetos a mi implementación .Net, defino un conjunto de clases: una clase base y varias clases secundarias (con una jerarquía compleja, que tiene 4 "generaciones"). Aquí hay solo un pequeño ejemplo de estas clases:

public abstract class TExpression
{
    [JsonProperty("type")]
    public string Type { get; set; }
}

public class TComment : TExpression
{
    [JsonProperty("text")]
    public string Text { get; set; }
}   

public class TTokenSequence : TExpression
{
    [JsonProperty("tokens")]
    public List<TToken> Tokens { get; set; }
}

Lo que quiero llegar es poder deserializar esta matriz en una lista genérica covariante, declarada como:

List<TExpression> myexpressions = JsonConvert.DeserializeObject<List<TExpression>>(aststring);

Esta lista debe contener las instancias de clases secundarias apropiadas que heredan de TExpression, por lo que puedo usar el siguiente código más adelante en mi código:

foreach(TExpression t in myexpressions)
{
    if (t is TComment) dosomething;
    if (t is TTokenSequence) dosomethingelse;
}

¿Cómo puedo llegar usando JSON.NET?

Answer 1

Aquí hay un ejemplo usando CustomCreationConverter.

public class JsonItemConverter :  Newtonsoft.Json.Converters.CustomCreationConverter<Item>
{
    public override Item Create(Type objectType)
    {
        throw new NotImplementedException();
    }

    public Item Create(Type objectType, JObject jObject)
    {
        var type = (string)jObject.Property("valueType");
        switch (type)
        {
            case "int":
                return new IntItem();
            case "string":
                return new StringItem();
        }

        throw new ApplicationException(String.Format("The given vehicle type {0} is not supported!", type));
    }

    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
        var target = Create(objectType, jObject);

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

        return target;
    }
}

public abstract class Item
{
    public string ValueType { get; set; }

    [JsonProperty("valueTypeId")]
    public int ValueTypeId { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    public new virtual string ToString() { return "Base object, we dont'' want base created ValueType=" + this.ValueType + "; " + "name: " + Name; }
}

public class StringItem : Item
{
    [JsonProperty("value")]
    public string Value { get; set; }

    [JsonProperty("numberChars")]
    public int NumberCharacters { get; set; }

    public override string ToString() { return "StringItem object ValueType=" + this.ValueType + ", Value=" + this.Value + "; " + "Num Chars= " + NumberCharacters; }

}

public class IntItem : Item
{
    [JsonProperty("value")]
    public int Value { get; set; }

    public override string ToString() { return "IntItem object ValueType=" + this.ValueType + ", Value=" + this.Value; }
}

class Program
{
    static void Main(string[] args)
    {
        // json string
        var json = "[{/"value/":5,/"valueType/":/"int/",/"valueTypeId/":1,/"name/":/"numberOfDups/"},{/"value/":/"some thing/",/"valueType/":/"string/",/"valueTypeId/":1,/"name/":/"a/",/"numberChars/":11},{/"value/":2,/"valueType/":/"int/",/"valueTypeId/":2,/"name/":/"b/"}]";

        // The above is deserialized into a list of Items, instead of a hetrogenous list of
        // IntItem and StringItem
        var result = JsonConvert.DeserializeObject<List<Item>>(json, new JsonItemConverter());

        foreach (var r in result)
        {
            // r is an instance of Item not StringItem or IntItem
            Console.WriteLine("got " + r.ToString());
        }
    }
}

Answer 2

También podría implementarse con JsonSubTypes de manera declarativa:

[JsonConverter(typeof(JsonSubtypes), "valueType")]
[JsonSubtypes.KnownSubType(typeof(IntItem), "int")]
[JsonSubtypes.KnownSubType(typeof(StringItem), "string")]
public abstract class Item
{
    public string ValueType { get; set; }

    [JsonProperty("valueTypeId")]
    public int ValueTypeId { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    public override string ToString()
    {
        return "Base object, we dont'' want base created ValueType=" + this.ValueType + "; " + "name: " + Name;
    }
}

public class StringItem : Item
{
    [JsonProperty("value")]
    public string Value { get; set; }

    [JsonProperty("numberChars")]
    public int NumberCharacters { get; set; }

    public override string ToString()
    {
        return "StringItem object ValueType=" + this.ValueType + ", Value=" + this.Value + "; " +
               "Num Chars= " + NumberCharacters;
    }
}

public class IntItem : Item
{
    [JsonProperty("value")]
    public int Value { get; set; }

    public override string ToString()
    {
        return "IntItem object ValueType=" + this.ValueType + ", Value=" + this.Value;
    }
}

[TestMethod]
public void Demo()
{
    // json string
    var json =
        "[{/"value/":5,/"valueType/":/"int/",/"valueTypeId/":1,/"name/":/"numberOfDups/"}," +
        "{/"value/":/"some thing/",/"valueType/":/"string/",/"valueTypeId/":1,/"name/":/"a/",/"numberChars/":11}," +
        "{/"value/":2,/"valueType/":/"int/",/"valueTypeId/":2,/"name/":/"b/"}]";

    var result = JsonConvert.DeserializeObject<List<Item>>(json);

    Assert.AreEqual("IntItem object ValueType=int, Value=5", result[0].ToString());
    Assert.AreEqual("StringItem object ValueType=string, Value=some thing; Num Chars= 11", result[1].ToString());
    Assert.AreEqual("IntItem object ValueType=int, Value=2", result[2].ToString());
}

Answer 3

CustomCreationConverter debería poder manejar esto.