How Can I Achieve Default Serialization in System.Text.Json Custom Converters Without Modifying the Write Method?

Use custom converter to handle default serialization

When creating a custom System.Text.Json.JsonConverter, you may not always need to modify the Write() method since you don't need any custom serialization. This article describes how to automatically generate default serialization to avoid using custom behavior in the Write() method.

Background

JsonConverter is applied to properties, objects or types according to their priority. The following situations exist:

• Custom converters applied to properties
• Converters added to the Converters collection
• Converters applied to custom value types or POCOs
• Converters returned by JsonConverterFactories

Each situation is handled differently.

Default serialization method

1. Converters applied to attributes:

• Default serialization can be generated by simply calling JsonSerializer.Serialize(writer, person, options).

2. Converters added to the Converters collection:

• Create a copy of JsonConverterOptions with the custom converter removed.
• Pass the modified copy to JsonSerializer.Serialize(Utf8JsonWriter, T, JsonSerializerOptions).
• Note that this approach can cause difficulties with recursive types.

3. Converters applied to custom value types or POCOs:

• There is no way to generate default serialization directly.

for convenient custom factories and extensions

To simplify the process, you can create a customizable factory that allows you to handle custom serialization without modifying the Write() method:

<code>public class DefaultConverterFactory<T> : JsonConverterFactory
{
    // 此处为内部 DefaultConverter 实现
}</code>

This factory serves as the basis for custom converters that manage the creation of copies of JsonSerializerOptions (custom converters have been removed). Modified options for default serialization in Write() method.

<code>public class PersonConverter : DefaultConverterFactory<Person>
{
    // 此处为 Read 和 Write 方法实现
}</code>

By using the DefaultConverterFactory base class, you can ensure that the Write() method performs default serialization while still maintaining custom behavior in the Read() method.

Other notes

• Applying DefaultConverterFactory directly to a custom value type or POCO will trigger a stack overflow.
• When trying to implement this method on a converter returned by a factory, it is important to determine whether to disable the entire factory or only for specific types.

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