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How to ignore properties with System.Text.Json

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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:

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 Main()
        {
            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 Main()
        {
            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 Main()
        {
            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