JSON deserialization - Map array indices to properties with JSON.NET

Question

I want to deserialize a 2-dimensional array to a collection of .net objects. The reason is, array syntax will be easier for my user to work with in an input file. So I just

Answer 1

You can do this with a JsonConverter. A simple converter for this purpose would be:

public class PersonConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Person);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;
        var array = JArray.Load(reader);
        var person = (existingValue as Person ?? new Person());
        person.First = (string)array.ElementAtOrDefault(0);
        person.Last = (string)array.ElementAtOrDefault(1);
        person.Age = (string)array.ElementAtOrDefault(2);
        return person;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var person = (Person)value;
        serializer.Serialize(writer, new[] { person.First, person.Last, person.Age });
    }
}

If the specific properties have non-primitive types, you can use JToken.ToObject<T>(JsonSerializer) to deserialize them to the required type:

person.First = array.ElementAtOrDefault(0)?.ToObject<string>(serializer);

Then you can apply it to your class:

[JsonConverter(typeof(PersonConverter))]
public class Person
{
    public string First { get; set; }
    public string Last { get; set; }
    public string Age { get; set; }
}

Or use it in settings:

var settings = new JsonSerializerSettings { Converters = new [] { new PersonConverter() } };
var list = JsonConvert.DeserializeObject<List<Person>>(json, settings);

Answer 2

    public override bool CanConvert(Type objectType)
    {
        if (objectType == typeof(List<Person>)) return true;

        return false;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        List<Person> persons = new List<Person>();

        JArray personsArray = (JArray)serializer.Deserialize(reader);

        foreach (var personArray in personsArray.Children<JArray>())
        {
            persons.Add(new Person() { 
                         First = personArray[0].Value<string>(),
                         Last = personArray[1].Value<string>(),
                         Age = personArray[2].Value<string>()
                        });
        }

        return persons;
    }