How Can I Preserve Default JSON Serialization Behavior in Custom JsonConverters?

Default serialization override in custom JsonConverter

Question

How to retain the default serialization behavior in a custom System.Text.Json.JsonConverter without custom writing logic?

Description

JsonConverter choices have different priorities, including:

• Attribute level features
• Converters added to the Converters collection
• Attributes that apply to custom value types or POCOs
• The converter returned by the converter factory

Solution

There are different ways to implement default serialization depending on how the converter is applied:

Attribute Level Features

Call JsonSerializer.Serialize(writer, person, options); will generate default serialization.

Converters in the Converters collection

• Copies the passed options, removing the converter from the copy's Converters list.
• Pass modified options to JsonSerializer.Serialize(Utf8JsonWriter, T, JsonSerializerOptions);
• Note: This method may not be thread-safe and may cause problems with recursive types.

Custom value type or POCO

• Currently, generating default serialization for converters applied to custom value types or POCOs is not supported.

Converter Factory

• Use DefaultConverterFactory to create a converter that generates default serialization.
• Cache modified options in manufactured converters that do not contain converters.

Example

Here is an example using a converter factory:

public sealed class PersonConverter : DefaultConverterFactory<Person>
{
    ...

    protected override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions modifiedOptions)
        => (T)JsonSerializer.Deserialize(ref reader, typeToConvert, modifiedOptions);

    protected override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions modifiedOptions) 
        => JsonSerializer.Serialize(writer, value, modifiedOptions);
}

...

var person = new Person("John", "Doe");
var options = new JsonSerializerOptions { Converters = { new PersonConverter() } };
var json = JsonSerializer.Serialize(person, options);

Important Note

• Applying DefaultConverterFactory directly to a custom value type or POCO will cause a stack overflow.
• Using JsonSerializer.Serialize(writer, person, options); will result in default serialization when applying a converter to property-level properties.

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