JsonNetDiscriminator

Lastest Version 0.0.1.375

What is JsonNetDiscriminator

This is a Newtonsoft JSON.NET extension that helps to face inheritance problems during JSON deserialization.

Suppose to have the following models.

public class Vehicle
{
    [JsonProperty(PropertyName = "color")]
    public string Color { get; set; }

    [JsonProperty(PropertyName = "dateOfRegistration")]
    public string DateOfRegistration { get; set; }
}

public class Van : Vehicle
{
    [JsonProperty(PropertyName = "carryingCapacity")]
    public decimal? CarryingCapacity { get; set; }
}

public class Car : Vehicle
{
    [JsonProperty(PropertyName = "ndoors")]
    public int? NumberOfDoors { get; set; }

    [JsonProperty(PropertyName = "engine")]
    public Engine CarEngine { get; set; }
}

Thanks to inheritance, in C# we don't have to declare a property that hold the information about the type of the object. Unluckly, JSON object declaration isn't as strict as C# one.

Now suppose that you have to deserialize the following JSON:

{ "color": "red", "dateOfRegistration": "2016-04-09", }

Looking at the object properties, you can infer that it could be deserialize into a Vehicle object.

And now?

{ "color": "red", "dateOfRegistration": "2016-04-09", "ndoors": 5 }

As we can see, into json there is the property ndoors which let us think about Car object but this isn't true into many other situations.

To have the certainty that we are speaking about a Car object, a discriminator property have to be added.

{ "type": "Car", "color": "red", "dateOfRegistration": "2016-04-09", "ndoors": 5 }

In this case, thanks to type property, we are sure that this JSON can be deserialize into a Car object.

And now JsonNetDiscriminator comes in handy.

You simply have to enrich Vehicle class with JsonPropertyDiscriminator attribute with the right matching types

[JsonPropertyDiscriminator("type", "Car", typeof(Car))]
[JsonPropertyDiscriminator("type", "Van", typeof(Van))]
public class Vehicle
{
    [JsonProperty(PropertyName = "color")]
    public string Color { get; set; }

    [JsonProperty(PropertyName = "dateOfRegistration")]
    public string DateOfRegistration { get; set; }
}

In this case we are saying that if the JSON contains the type property with its value Car, this JSON can be deserialize into a Car object. If the value is Van, into a Van object.

Calling JSON deserialization method

var vehicle = JsonConvert.DeserializeObject<Vehicle>(json, new JsonDiscriminatorConverter(typeof(Vehicle)));

vehicle will be a Car object.