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:

C#

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

JSON

{
  "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:

C#

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}

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:

C#

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

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

C#

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;
}

JSON

{
  "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.

Note

Read-only collection-type properties are still serialized even if JsonSerializerOptions.IgnoreReadOnlyProperties is set to true.

Ignore all null-value properties

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

C#

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}

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:

C#

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"}

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