using System;

using System.Collections.Generic;

using Newtonsoft.Json;

using Newtonsoft.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var myUserFieldValues = new List<CustomField>(){

            new CustomField(){

                CustomFieldID = "groc 1",

                Value = "truffles"

            },

             new CustomField(){

                CustomFieldID = "groc 2",

                Value = "some thing"

            },          

        };

        var myLineItem = new LineItem() {

            PartID = 1,

            Quantity= 2,

            Comments = "something",

            CustomFields = myUserFieldValues

        };

​

    //  JsonSerializerSettings jsonSettings = new JsonSerializerSettings();

    //  jsonSettings.ContractResolver = new CustomOrderLineResolver();

        JsonConvert.SerializeObject(myLineItem).Dump();

        //Actual Value 

        //{"part":1,"quant":2,"comments":"something","CustomFields":[{"key":"groc 1","value":"truffles"},{"key":"groc 2","value":"some thing"}]}

        //Desired Value

        //{"part":1,"quant":2,"comments":"something","groc 1", "truffles", "groc 2", "some thing"}

    }

    public class LineItem

    {

        [JsonProperty("part")]

        public int PartID { get; set; }

        [JsonProperty("quant")]

        public int Quantity { get; set; }

        [JsonProperty("comments")]

        public string Comments { get; set; }

        public List<CustomField> CustomFields { get; set; }

    }

    public class CustomField

    {

        [JsonProperty("key")]

        public string CustomFieldID { get; set; }

        [JsonProperty("value")]

        public string Value { get; set; }

    }

​

}

​