Json_serializable.dart: Allow deserialize into subclasses

[fzyzcjy]

Hi, thanks for the wonderful library! This is like a feature request since there seems no existing supply.

For instance, suppose we have (ignoring unrelated details):

class A { Animal animal; String fieldInA;}
abstract class Animal { String fieldInBaseClass; }
class Dog extends Animal { String name; }
class Human extends Animal { int id; }

Then I want to serialize and de-serialize the "animal" into concrete classes. For instance, the following object:

A a1 = A(animal: Dog(fieldInBaseClass: 'base', name: 'hi'), fieldInA:'a');
A a2= A(animal: Human(fieldInBaseClass: 'base', id: 42), fieldInA:'a');

should be able to be converted back and forth with the following json string:

{fieldInA: 'a', animal: {type: 'Dog', fieldInBaseClass: 'base', name: 'hi'}}
{fieldInA: 'a', animal: {type: 'Human', fieldInBaseClass: 'base', id: 42}}

Thanks very much for any reply!

[kevmoo]

You could absolutely create factory Animal.fromJson(...) { ... } that inspects the JSON content and forwards to right subclass fromJson.

[fzyzcjy]

@kevmoo Thanks! However, it is not automated...?

[kevmoo]

Doing this in an automated way would be very complex. we are actively
avoiding adding a lot of new complexity to this package just to make sure
maintenance stays consistent.

On Thu, Jan 30, 2020, 15:36 fzyzcjy [e-mail] wrote:

@kevmoo https://github.com/kevmoo Thanks! However, it is not
automated...?

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[fzyzcjy]

Ah fine... So I may implement it by myself. Thanks

[fzyzcjy]

@kevmoo My proposal on syntax and implementations are as follows, which I think is too straightforward to be true... Is this fine? Or will I meet some problems?

1. Annotate the subclasses

@Subclasses([Dog, Human])
abstract class Animal {}

1. Then use this directly in the code generator (just some rough idea, not runnable code):

List<Type> subclasses = getTheSubclassesAnnotation();
writeDownTheCode('switch(data["type"]) {');
for(var subclass in subclasses) {
    writeDownTheCode('case $subclass: return $subclass.fromJson(data['payload']);');
}
writeDownTheCode('}');