How to ignore properties with System.Text.Json

When serializing C# objects to JavaScript Object Notation (JSON), by default, all public properties are serialized. If you don't want some of them to appear in the resulting JSON, you have several options. In this article, you learn how to ignore properties based on various criteria:

• Individual properties
• All read-only properties
• All null-value properties
• All default-value properties

Ignore individual properties

To ignore individual properties, use the [JsonIgnore] attribute.

The following example shows a type to serialize. It also shows the JSON output:

public class WeatherForecastWithIgnoreAttribute
{
 public DateTimeOffset Date { get; set; }
 public int TemperatureCelsius { get; set; }
 [JsonIgnore]
 public string? Summary { get; set; }
}

Public Class WeatherForecastWithIgnoreAttribute
 Public Property [Date] As DateTimeOffset
 Public Property TemperatureCelsius As Integer

 <JsonIgnore>
 Public Property Summary As String

End Class

{
 "Date": "2019-08-01T00:00:00-07:00",
 "TemperatureCelsius": 25,
}

You can specify conditional exclusion by setting the [JsonIgnore] attribute's Condition property. The JsonIgnoreCondition enum provides the following options:

• Always - The property is always ignored. If no Condition is specified, this option is assumed.
• Never - The property is always serialized and deserialized, regardless of the DefaultIgnoreCondition, IgnoreReadOnlyProperties, and IgnoreReadOnlyFields global settings.
• WhenWritingDefault - The property is ignored on serialization if it's a reference type null, a nullable value type null, or a value type default.
• WhenWritingNull - The property is ignored on serialization if it's a reference type null, or a nullable value type null.

The following example illustrates the use of the [JsonIgnore] attribute's Condition property:

using System.Text.Json;
using System.Text.Json.Serialization;

namespace JsonIgnoreAttributeExample
{
 public class Forecast
 {
 [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
 public DateTime Date { get; set; }

 [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
 public int TemperatureC { get; set; }

 [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
 public string? Summary { get; set; }
 };

 public class Program
 {
 public static void Run()
 {
 Forecast forecast = new()
 {
 Date = default,
 Summary = null,
 TemperatureC = default
 };

 JsonSerializerOptions options = new()
 {
 DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault
 };

 string forecastJson =
 JsonSerializer.Serialize<Forecast>(forecast,options);

 Console.WriteLine(forecastJson);
 }
 }
}

// Produces output like the following example:
//
//{"TemperatureC":0}

Imports System.Text.Json
Imports System.Text.Json.Serialization

Namespace JsonIgnoreAttributeExample

 Public Class Forecast

 <JsonIgnore(Condition:=JsonIgnoreCondition.WhenWritingDefault)>
 Public Property [Date] As Date

 <JsonIgnore(Condition:=JsonIgnoreCondition.Never)>
 Public Property TemperatureC As Integer

 <JsonIgnore(Condition:=JsonIgnoreCondition.WhenWritingNull)>
 Public Property Summary As String

 End Class

 Public NotInheritable Class Program

 Public Shared Sub Main()
 Dim forecast1 As New Forecast() With {
 .[Date] = CType(Nothing, Date),
 .Summary = Nothing,
 .TemperatureC = CType(Nothing, Integer)
 }

 Dim options As New JsonSerializerOptions() With {
 .DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault
 }

 Dim forecastJson As String = JsonSerializer.Serialize(forecast1, options)

 Console.WriteLine(forecastJson)
 End Sub

 End Class

End Namespace

' Produces output like the following example:
'
'{"TemperatureC":0}

Ignore all read-only properties

A property is read-only if it contains a public getter but not a public setter. To ignore all read-only properties when serializing, set the JsonSerializerOptions.IgnoreReadOnlyProperties to true, as shown in the following example:

var options = new JsonSerializerOptions
{
 IgnoreReadOnlyProperties = true,
 WriteIndented = true
};
jsonString = JsonSerializer.Serialize(weatherForecast, options);

Dim options As JsonSerializerOptions = New JsonSerializerOptions With {
 .IgnoreReadOnlyProperties = True,
 .WriteIndented = True
}
jsonString = JsonSerializer.Serialize(weatherForecast, options)

The following example shows a type to serialize. It also shows the JSON output:

public class WeatherForecastWithROProperty
{
 public DateTimeOffset Date { get; set; }
 public int TemperatureCelsius { get; set; }
 public string? Summary { get; set; }
 public int WindSpeedReadOnly { get; private set; } = 35;
}

Public Class WeatherForecastWithROProperty
 Public Property [Date] As DateTimeOffset
 Public Property TemperatureCelsius As Integer
 Public Property Summary As String
 Private _windSpeedReadOnly As Integer

 Public Property WindSpeedReadOnly As Integer
 Get
 Return _windSpeedReadOnly
 End Get
 Private Set(Value As Integer)
 _windSpeedReadOnly = Value
 End Set
 End Property

End Class

{
 "Date": "2019-08-01T00:00:00-07:00",
 "TemperatureCelsius": 25,
 "Summary": "Hot",
}

This option applies only to properties. To ignore read-only fields when serializing fields, use the JsonSerializerOptions.IgnoreReadOnlyFields global setting.

Ignore all null-value properties

To ignore all null-value properties, set the DefaultIgnoreCondition property to WhenWritingNull, as shown in the following example:

using System.Text.Json;
using System.Text.Json.Serialization;

namespace IgnoreNullOnSerialize
{
 public class Forecast
 {
 public DateTime Date { get; set; }
 public int TemperatureC { get; set; }
 public string? Summary { get; set; }
 };

 public class Program
 {
 public static void Run()
 {
 Forecast forecast = new()
 {
 Date = DateTime.Now,
 Summary = null,
 TemperatureC = default
 };

 JsonSerializerOptions options = new()
 {
 DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
 };

 string forecastJson =
 JsonSerializer.Serialize<Forecast>(forecast, options);
 
 Console.WriteLine(forecastJson);
 }
 }
}

// Produces output like the following example:
//
//{"Date":"2020-10-30T10:11:40.2359135-07:00","TemperatureC":0}

Imports System.Text.Json

Namespace IgnoreNullOnSerialize

 Public Class Forecast
 Public Property [Date] As Date
 Public Property TemperatureC As Integer
 Public Property Summary As String
 End Class

 Public NotInheritable Class Program

 Public Shared Sub Main()
 Dim forecast1 As New Forecast() With
 {
 .[Date] = Date.Now,
 .Summary = Nothing,
 .TemperatureC = CType(Nothing, Integer)
 }

 Dim options As New JsonSerializerOptions

 Dim forecastJson As String = JsonSerializer.Serialize(forecast1, options)

 Console.WriteLine(forecastJson)
 End Sub

 End Class

End Namespace

' Produces output like the following example:
'
'{"Date":"2020-10-30T10:11:40.2359135-07:00","TemperatureC":0}

Ignore all default-value properties

To prevent serialization of default values in value type properties, set the DefaultIgnoreCondition property to WhenWritingDefault, as shown in the following example:

using System.Text.Json;
using System.Text.Json.Serialization;

namespace IgnoreValueDefaultOnSerialize
{
 public class Forecast
 {
 public DateTime Date { get; set; }
 public int TemperatureC { get; set; }
 public string? Summary { get; set; }
 };

 public class Program
 {
 public static void Run()
 {
 Forecast forecast = new()
 {
 Date = DateTime.Now,
 Summary = null,
 TemperatureC = default
 };

 JsonSerializerOptions options = new()
 {
 DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault
 };

 string forecastJson =
 JsonSerializer.Serialize<Forecast>(forecast, options);

 Console.WriteLine(forecastJson);
 }
 }
}

// Produces output like the following example:
//
//{ "Date":"2020-10-21T15:40:06.8920138-07:00"}

Imports System.Text.Json
Imports System.Text.Json.Serialization

Namespace IgnoreValueDefaultOnSerialize

 Public Class Forecast
 Public Property [Date] As Date
 Public Property TemperatureC As Integer
 Public Property Summary As String
 End Class

 Public NotInheritable Class Program

 Public Shared Sub Main()
 Dim forecast1 As New Forecast() With
 {.[Date] = Date.Now,
 .Summary = Nothing,
 .TemperatureC = CType(Nothing, Integer)
 }

 Dim options As New JsonSerializerOptions() With {
 .DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault
 }

 Dim forecastJson As String = JsonSerializer.Serialize(forecast1, options)

 Console.WriteLine(forecastJson)
 End Sub

 End Class

End Namespace

' Produces output like the following example:
'
'{ "Date":"2020-10-21T15:40:06.8920138-07:00"}

The WhenWritingDefault setting also prevents serialization of null-value reference type and nullable value type properties.

See also

• System.Text.Json overview
• How to serialize and deserialize JSON