.NET 5 Ignore Properties

When serializing C# objects to JSON, by default, all public properties are serialized. If you don't want some of them to appear in the resulting JSON, you have the following options.

• Ignore Individual Properties
• Ignore All Read-only Properties
• Ignore All Null-value Properties
• Ignore All Default-value Properties

Ignore Individual Properties

To ignore individual properties, you can use the [JsonIgnore] attribute to prevents a property from being serialized or deserialized.

public class Customer
{
    public string Name { get; set; }

    public int Age { get; set; }

    [JsonIgnore]
    public string? Address { get; set; }
};

public static void Example1()
{
    Customer customer = new()
    {
        Name = "Mark",
        Address = "22 wall street.",
        Age = 23
    };

    string json = JsonSerializer.Serialize<Customer>(customer);

    Console.WriteLine(json);
}

The above example will print the following output.

{"Name":"Mark","Age":23}

You can also 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 is a reference type null, a nullable value type null, or a value type default.
• WhenWritingNull: The property is ignored on serialization if it is a reference type null, or a nullable value type null.

The following example shows the usage of the [JsonIgnore] attribute with a condition property.

public class Customer2
{
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    public string Name { get; set; }

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

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

public static void Example2()
{
    Customer2 customer = new()
    {
        Name = default,
        Address = null,
        Age = default
    };

    string json = JsonSerializer.Serialize<Customer2>(customer);

    Console.WriteLine(json);
}

The above example will print the following output.

{"Age":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 below.

public class Customer3
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string? Address { get; set; }
    public DateTime? DOB { get; private set; }

    public Customer3(string name, int age, string address, DateTime dob)
    {
        (Name, Age, Address, DOB) = (name, age, address, dob);
    }
};

public static void Example3()
{
    Customer3 customer = new("Mark", 31, "22 wall street.", DateTime.Now.AddYears(-29));

    var options = new JsonSerializerOptions
    {
        IgnoreReadOnlyProperties = true,
        WriteIndented = true
    };

    string json = JsonSerializer.Serialize<Customer3>(customer, options);

    Console.WriteLine(json);
}

The above example will print the following output.

{
  "Name": "Mark",
  "Age": 31,
  "Address": "22 wall street."
}

This option applies only to serialization. During deserialization, read-only properties are ignored by default.

Ignore All Null-value Properties

To ignore all null-value properties, set the DefaultIgnoreCondition property to WhenWritingNull, as shown below.

public class Customer4
{
    public string Name { get; set; }

    public int Age { get; set; }

    public string? Address { get; set; }
};

public static void Example4()
{
    Customer4 customer = new()
    {
        Name = "Mark",
        Address = null,
        Age = 23
    };

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


    string json = JsonSerializer.Serialize<Customer4>(customer, options);

    Console.WriteLine(json);
}

The above example will print the following output.

{"Name":"Mark","Age":23}

Ignore All Default-value Properties

To prevent serialization of default values in value type properties, set the DefaultIgnoreCondition property to WhenWritingDefault, as shown below.

public class Customer5
{
    public string Name { get; set; }

    public int Age { get; set; }

    public string? Address { get; set; }
    public DateTime? DOB { get; set; }
};

public static void Example5()
{
    Customer5 customer = new()
    {
        Name = "Mark",
        Address = "11 wall street.",
        Age = 25,
        DOB = default
    };

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


    string json = JsonSerializer.Serialize<Customer5>(customer, options);

    Console.WriteLine(json);
}

The above example will print the following output.

{"Name":"Mark","Age":25,"Address":"11 wall street."}