c# - Is it possible to catch somehow the remainder of JSON data that didn't match any POCO properties while deserializing?

Question

I'm getting some JSON data from the external API. I have my POCO objects to which the data is deserialized. I use System.Text.Json.JsonSerializer for deserialization. Recently, I realized that the structure of the JSON that I receive has changed and I got to know it only by accident while checking something else. My question is, is it possible to catch somehow the json data that didn't succeed to be mapped to any POCO fields?

To be more precise with my question here is an example POCO:

public class Car
{
    public string Name { get; set; }
    public int Age { get; set; }
}

JSON that I received before:

{"Name" : "PinkCar", "Age": 3}

JSON that I receive now:

{"Name" : "PinkCar", "Age": 3, "RogueField": "Loser"}

I would like to be able to at least get somehow information that there is this new "RogueField" that doesn't match any POCO properties without breaking the process of deserialization.

Answer 1

Extra properties can be saved in a dictionary with your object. You can manipulate this directory and it will be used when serializing your object again.

From https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-how-to#handle-overflow-json: Create a property of the type Dictionary<string, object>, this can have any name (mostly this is named ExtensionData but can be anything), and decorate it with the [JsonExtensionData] attribute, for example:

public class Car
{
    public string Name { get; set; }
    public int Age { get; set; }
    [JsonExtensionData]
    public Dictionary<string, object> ExtensionData { get; set; }
}