Ignore a property when deserializing using Json.Net with ItemRequired = Required.Always

Question

I'm using Json.Net to serialize and deserialize classes to json and back.

I added to a class marked with [JsonObject(ItemRequired = Required.Always)] (or Required.Always) a new get-only property. That results in the following JsonSerializationException:

Newtonsoft.Json.JsonSerializationException: Required property '<PropertyName>' not found in JSON

I thought marking that property with JsonIgnore would solve the issue, but that doesn't work.

How can I tell Json.Net that this property should be ignored?

Here's a minimal example reproducing the issue:

[JsonObject(ItemRequired = Required.Always)]
public class Hamster
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    [JsonIgnore]
    public string FullName { get { return FirstName + LastName; }}
}

private static void Main()
{
    var hamster = new Hamster {FirstName = "Bar", LastName = "Arnon"};
    var serializeObject = JsonConvert.SerializeObject(hamster);
    var deserializeObject = JsonConvert.DeserializeObject<Hamster>(serializeObject);
}

Solution

Evidently JsonIgnore will only control the serialization in this case. JsonIgnore is required to specify that the FullName property should not be serialized to the json representation.

To ignore the property during deserialization we need to add the JsonProperty annotation with Required = Required.Default (which means not required).

So, this is how to avoid the JsonSerializationException:

[JsonObject(ItemRequired = Required.Always)]
public class Hamster
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    [JsonIgnore]
    [JsonProperty(Required = Required.Default)]
    public string FullName { get { return FirstName + LastName; }}
}

Comments

[nAviD]

why there is no JsonPropertyAttribute in Json.Net (.net core 5)?

[i3arnon]

@nAviD there is. Just checked. I assume you're not actually using Json.NET.