在我的情况下，使用。net 6这是解决方案:

[JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]

更多信息请点击这里。

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.

在。net Core中，这就容易多了。在你的startup.cs中添加json选项，你可以在那里配置设置。

public void ConfigureServices(IServiceCollection services)

....

services.AddMvc().AddJsonOptions(options =>
{
   options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;               
});

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
// }

对于System.Text.Json和.NET Core 3.0，这对我来说是可行的:

var jsonSerializerOptions = new JsonSerializerOptions()
{
    IgnoreNullValues = true
};
var myJson = JsonSerializer.Serialize(myObject, jsonSerializerOptions );

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);