这并没有完全回答最初的问题，但根据用例可能证明是有用的。(因为我是在搜索之后才来到这里的，所以它可能对其他人有用。)

在我最近的经验中，我正在使用PATCH api。如果指定了一个属性但没有给定值(null/undefined，因为它是js)，那么该属性和值将从正在修补的对象中移除。所以我在寻找一种方法来选择性地构建一个对象，它可以以这样一种方式序列化，这样就可以工作。

我记得看到过ExpandoObject，但直到今天才有一个真正的用例。这允许您动态地构建对象，因此您不会有null属性，除非您希望它们在那里。

这是一个工作提琴，与下面的代码。

结果:

Standard class serialization
    noName: {"Name":null,"Company":"Acme"}
    noCompany: {"Name":"Fred Foo","Company":null}
    defaultEmpty: {"Name":null,"Company":null}
ExpandoObject serialization
    noName: {"Company":"Acme"}
    noCompany: {"name":"Fred Foo"}
    defaultEmpty: {}

代码:

using Newtonsoft.Json;
using System;
using System.Dynamic;
                    
public class Program
{
    public static void Main()
    {
        SampleObject noName = new SampleObject() { Company = "Acme" };
        SampleObject noCompany = new SampleObject() { Name = "Fred Foo" };
        SampleObject defaultEmpty = new SampleObject();
        
        
        Console.WriteLine("Standard class serialization");
        Console.WriteLine($"    noName: { JsonConvert.SerializeObject(noName) }");
        Console.WriteLine($"    noCompany: { JsonConvert.SerializeObject(noCompany) }");
        Console.WriteLine($"    defaultEmpty: { JsonConvert.SerializeObject(defaultEmpty) }");
        
        
        Console.WriteLine("ExpandoObject serialization");
        Console.WriteLine($"    noName: { JsonConvert.SerializeObject(noName.CreateDynamicForPatch()) }");
        Console.WriteLine($"    noCompany: { JsonConvert.SerializeObject(noCompany.CreateDynamicForPatch()) }");
        Console.WriteLine($"    defaultEmpty: { JsonConvert.SerializeObject(defaultEmpty.CreateDynamicForPatch()) }");
    }
}

public class SampleObject {
    public string Name { get; set; }
    public string Company { get; set; }
    
    public object CreateDynamicForPatch()
    {
        dynamic x = new ExpandoObject();
        
        if (!string.IsNullOrWhiteSpace(Name))
        {
            x.name = Name;
        }
        
        if (!string.IsNullOrEmpty(Company))
        {
            x.Company = Company;
        }
        
        return x;
    }
}

可以在他们的网站(http://james.newtonking.com/archive/2009/10/23/efficient-json-with-json-net-reducing-serialized-json-size.aspx)上的这个链接中看到，我支持使用[Default()]来指定默认值

摘自链接

   public class Invoice
{
  public string Company { get; set; }
  public decimal Amount { get; set; }

  // false is default value of bool
  public bool Paid { get; set; }
  // null is default value of nullable
  public DateTime? PaidDate { get; set; }

  // customize default values
  [DefaultValue(30)]
  public int FollowUpDays { get; set; }
  [DefaultValue("")]
  public string FollowUpEmailAddress { get; set; }
}


Invoice invoice = new Invoice
{
  Company = "Acme Ltd.",
  Amount = 50.0m,
  Paid = false,
  FollowUpDays = 30,
  FollowUpEmailAddress = string.Empty,
  PaidDate = null
};

string included = JsonConvert.SerializeObject(invoice,
  Formatting.Indented,
  new JsonSerializerSettings { });

// {
//   "Company": "Acme Ltd.",
//   "Amount": 50.0,
//   "Paid": false,
//   "PaidDate": null,
//   "FollowUpDays": 30,
//   "FollowUpEmailAddress": ""
// }

string ignored = JsonConvert.SerializeObject(invoice,
  Formatting.Indented,
  new JsonSerializerSettings { DefaultValueHandling = DefaultValueHandling.Ignore });

// {
//   "Company": "Acme Ltd.",
//   "Amount": 50.0
// }

使用JsonProperty属性的替代解决方案:

[JsonProperty(NullValueHandling=NullValueHandling.Ignore)]
// or
[JsonProperty("property_name", NullValueHandling=NullValueHandling.Ignore)]

// or for all properties in a class
[JsonObject(ItemNullValueHandling = NullValueHandling.Ignore)]

在这个在线文档中可以看到。

与Json。网

 public class Movie
 {
            public string Name { get; set; }
            public string Description { get; set; }
            public string Classification { get; set; }
            public string Studio { get; set; }
            public DateTime? ReleaseDate { get; set; }
            public List<string> ReleaseCountries { get; set; }
 }

 Movie movie = new Movie();
 movie.Name = "Bad Boys III";
 movie.Description = "It's no Bad Boys";

 string ignored = JsonConvert.SerializeObject(movie,
            Formatting.Indented,
            new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore });

结果将是:

{
   "Name": "Bad Boys III",
   "Description": "It's no Bad Boys"
 }

var settings = new JsonSerializerSettings();
settings.ContractResolver = new CamelCasePropertyNamesContractResolver();
settings.NullValueHandling = NullValueHandling.Ignore;
//you can add multiple settings and then use it
var bodyAsJson = JsonConvert.SerializeObject(body, Formatting.Indented, settings);

这里有一个类似的选项，但提供了另一种选择:

public class DefaultJsonSerializer : JsonSerializerSettings
{
    public DefaultJsonSerializer()
    {
        NullValueHandling = NullValueHandling.Ignore;
    }
}

然后，我这样使用它:

JsonConvert.SerializeObject(postObj, new DefaultJsonSerializer());

不同之处在于:

Reduces repeated code by instantiating and configuring JsonSerializerSettings each place it's used. Saves time in configuring every property of every object to be serialized. Still gives other developers flexibility in serialization options, rather than having the property explicitly specified on a reusable object. My use-case is that the code is a 3rd party library and I don't want to force serialization options on developers who would want to reuse my classes. Potential drawbacks are that it's another object that other developers would need to know about, or if your application is small and this approach wouldn't matter for a single serialization.