JsonProperty on C# Records in Constructor [duplicate]

Question

With the new C# record types in C# 9 i'd like to know wheter it is possible (for serialization) to set the JsonPropertyAttribute from Newtonsoft.Json on the constructor parameter. It doesn't seem to work out of the box.

MWE:

using System;
using Newtonsoft.Json;

Console.WriteLine(JsonConvert.SerializeObject(new Something("something")));

record Something([JsonProperty("hello")] string world) {}

Output:

{"world":"something"}

Expected output:

{"hello":"something"}

is there an easy way to make it work like this? or do we have to revert back to the property style with a real constructor?

internal record Something
{
    public Something(string world) { World = world; }

    [JsonProperty("hello")] public string World { get; }
}

Answer 1

Per the docs:

Attributes can be applied to the synthesized auto-property and its backing field by using property: or field: targets for attributes syntactically applied to the corresponding record parameter.

So you want

record Something([property:JsonProperty("hello")] string world) {}

Without the property: qualifier, the attribute ends up on the parameter of the generated constructor (which is useful in other scenarios, like nullability).