C# Json deserialize integer to type instance

Question

Consider the following json string given:

{
    "items":
    [
        { 
            ..., 
            "view_count":4,
            "answer_count":0,
            "score":0,
            "last_activity_date":1445071150
        }
    ],
    ...
}

Is there a way to have last_activity_date deserialized as instance of another type using System.Runtime.Serialization.DataContractAttribute and System.Runtime.Serialization.Json.DataContractJsonSerializer?

E.g.: 1445071150 -> Date where Date is

[System.Runtime.Serialization.DataContract]
public class Date
{
    [System.Runtime.Serialization.IgnoreDataMember]
    public long ElapsedSeconds { get; set; }

    [System.Runtime.Serialization.IgnoreDataMember]
    public DateTime Date { get { ... } set; }

    public Date(long seconds)
    {
        ElapsedSeconds = seconds;
        Date = ...;
    }

    public static implicit operator Date(long seconds)
    {
        return new Date(seconds);
    }

    // Other members ...
}

Answer 1

You could have a definition like that:

[DataContract]
public class Item
{
    [DataMember(Name = "view_count")]
    public int ViewCount { get; set; }

    [DataMember(Name = "answer_count")]
    public int AnswerCount { get; set; }

    [DataMember(Name = "score")]
    public int Score { get; set; }

    [IgnoreDataMember]
    public Date LastActivityDate { get; private set; }

    [DataMember(Name = "last_activity_date")]
    private long Date
    {
        set
        {
            LastActivityDate = value;
        }
        get
        {
            return LastActivityDate.ElapsedSeconds;
        }
    }
}

Now when the JSON is deserialized, the setter of the Date property will take care of setting the LastActivityDate member.

And here's a full example:

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Json;
using System.Text;

[DataContract]
public class Root
{
    [DataMember(Name = "items")]
    public Item[] Items { get; set; }
}

[DataContract]
public class Item
{
    [DataMember(Name = "view_count")]
    public int ViewCount { get; set; }

    [DataMember(Name = "answer_count")]
    public int AnswerCount { get; set; }

    [DataMember(Name = "score")]
    public int Score { get; set; }

    [IgnoreDataMember]
    public Date LastActivityDate { get; private set; }

    [DataMember(Name = "last_activity_date")]
    private long Date
    {
        set
        {
            LastActivityDate = value;
        }
        get
        {
            return LastActivityDate.ElapsedSeconds;
        }
    }
}

[DataContract]
public class Date
{
    [IgnoreDataMember]
    public long ElapsedSeconds { get; set; }

    public Date(long seconds)
    {
        ElapsedSeconds = seconds;
    }

    public static implicit operator Date(long seconds)
    {
        return new Date(seconds);
    }
}

static class Program
{
    static void Main()
    {
        string json = 
            @"{
                ""items"":
                [
                    { 
                        ""view_count"":4,
                        ""answer_count"":0,
                        ""score"":0,
                        ""last_activity_date"":1445071150
                    }
                ]
            }";

        var serializer = new DataContractJsonSerializer(typeof(Root));
        using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(json)))
        {
            var root = (Root)serializer.ReadObject(stream);
            Console.WriteLine(root.Items[0].LastActivityDate.ElapsedSeconds);
        }
    }
}