How to Create a Custom JsonConverter in JSON.NET to Handle Polymorphic Serialization without TypeNameHandling?

Implement customized JSONCONVERRTER

in json.net

Custom JSONCONVERTER is used to extend json.net serialization and dependentization functions. In some cases, custom converters need to be created to process complex or customized data types.

Let's consider an example, where you have a base class Person and two derived Employee and Artist. You have a list of Person objects that need to be serialized as JSON. However, you want to avoid using TypenameHandling. This is where the custom JSONCONVERTER can play a role.

For this reason, we need to define a custom converter PersonConverter, which expands the JSONCREATIONVERter

. In the Create method of the converter, we can analyze the JSON object to determine the correct derivative type according to the existence of specific fields.

public class PersonConverter : JsonCreationConverter<Person>
{
    protected override Person Create(Type objectType, JObject jObject)
    {
        if (FieldExists("Skill", jObject))
        {
            return new Artist();
        }
        else if (FieldExists("Department", jObject))
        {
            return new Employee();
        }
        else
        {
            return new Person();
        }
    }

    private bool FieldExists(string fieldName, JObject jObject)
    {
        return jObject[fieldName] != null;
    }
}

Now, when the JSON backflow is serialized back to the list

object, you can use a custom converter:

string json = "[...]";
List<Person> persons = JsonConvert.DeserializeObject<List<Person>>(json, new PersonConverter());

Remember that when using a custom converter during the sequentialization, the instance of the PersonConverter needs to be passed to JSONCONVERT.DeserializeObject. This method allows you to process complex or customized data types by providing special conversion logic in a custom JSONCONVERRER.

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