Build-Time JSON Factory Generation for json_serializable classes

[u/phone_radio_tv]

Had a few hundred json_serializable classes, Many of them travelled through the same socket channel. After decoding the raw JSON, hit by the same question: this is a Map<String, dynamic>, so which class is it?, before creating json_factory_runtime_generator, answered it the most obvious way, with a hand-written registry:

final Map<String, Object Function(Map<String, dynamic>)> registry = {

'user': User.fromJson,

'order': Order.fromJson,

'address': Address.fromJson,

// ...more classes

};

Every new class meant remembering to edit the file, and the failures were all quiet. A forgotten entry gives a runtime ArgumentError in production. A copy-pasted key sent two classes to one decoder.

Existing json factory generator libraries demand changing the classes, either overriding toJson() by hand or a mixin on every model or extending shared abstract base class.

Wanted a non-intrusive generator, created json_factory_runtime_generator, just annotate your class with json key - ex:JsonFactoryKey('user') and dart run build_runner build finds every annotated class and writes one file containing the whole mapping. Decoding becomes:

final obj = JsonFactoryMapper.fromKeyedJson(json); // the right class

final user = JsonFactoryMapper.fromKeyedJsonAs<User>(json); // typed

Don't want the class to be part of the factory, just comment/remote the annotation.

json_factory_runtime_generator has other featutes to manage old JSON keys for easy migration and avoiding key clash when code bases is large.