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 );

.Net 6 - 在Program.cs中添加代码。这将忽略类或记录属性，如果它是空的。

using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers()
.AddJsonOptions(opts =>
{
    var enumConverter = new JsonStringEnumConverter();
    opts.JsonSerializerOptions.Converters.Add(enumConverter);
    opts.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault | JsonIgnoreCondition.WhenWritingNull;
});

你可以写:[JsonProperty("property_name"，DefaultValueHandling = DefaultValueHandling. ignore)]

它还负责使用默认值(不仅仅是null)不序列化属性。例如，它对枚举很有用。

JSON。NET也尊重DataMemberAttribute上的EmitDefaultValue属性，以防你不想将newtonsoft特定的属性添加到你的模型中:

[DataMember(Name="property_name", EmitDefaultValue=false)]

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"
 }