JsonPropertyAttribute items setting

public class Business
{
    public string Name { get; set; }

    [JsonProperty(ItemIsReference = true)]
    public IList<Employee> Employees { get; set; }
}

public class Employee
{
    public string Name { get; set; }

    [JsonProperty(IsReference = true)]
    public Employee Manager { get; set; }
}

Employee manager = new Employee
{
    Name = "George-Michael"
};
Employee worker = new Employee
{
    Name = "Maeby",
    Manager = manager
};

Business business = new Business
{
    Name = "Acme Ltd.",
    Employees = new List<Employee>
    {
        manager,
        worker
    }
};

string json = JsonConvert.SerializeObject(business, Formatting.Indented);

Console.WriteLine(json);
// {
//   "Name": "Acme Ltd.",
//   "Employees": [
//     {
//       "$id": "1",
//       "Name": "George-Michael",
//       "Manager": null
//     },
//     {
//       "$id": "2",
//       "Name": "Maeby",
//       "Manager": {
//         "$ref": "1"
//       }
//     }
//   ]
// }