Possibility to extend base Model with well-known fields (TypeScript)

[Arsync]

Hello! Pinia ORM describes Single Table Inheritance. But what if we just need to provide some well-known fields to all derived models?

For example, I have another base class ManagedModel, which is extended from Model and provides two fields: id: string and $hasChanges: boolean. It is not part of STI, just known fields (which is not working for now - always has it's value as undefined):

import { Model } from 'pinia-orm';

/* abstract */ class ManagedModel extends Model
{
    static managedEntity: string; // for auto-navigation purpose by convention, singular entity name.

    static fields()
    {
        return {
            id: this.string(''), // Issue: always undefined in sub-entities
            $hasChanges: this.boolean(false)  // Issue: always undefined in sub-entities
        };
    }

    id!: string;

    $hasChanges!: boolean;
}

export { ManagedModel };

Sub-entities of ManagedModel is used as root models for ModelManager, which is proxy-based wrapper for all nested field changes to update store and backup (Dexie) with debounced user input (450 ms).

export function useModelProxy<TManagedModel extends ManagedModel>(
    model: TManagedModel,
    options: IModelProxyOptions
)
{
  const repo = useRepo(model.$self()); // Ok.
  const query = repo.where('id', model['id']); // Need to strongly type id, defined on model

  // lodash-es/debounce
  const onPropertyChanged = debounce(
    (target: Model, key: string, value: unknown) =>
    {
      query.update({
        [key]: value,
        $hasChanges: true // Special field
      });

      // There is some logic to put field in Dexie.
      // Dexie is need to know id. But we can't guarantee that it is field with name "id".
      // In vuex-orm it was special model.$id field.
      // We have model.$primaryKey(), but it's type is "string | string[]".
    },
    options.wait,
    { maxWait: options.maxWait }
  );

  // Omitted code, new Proxy with get and set traps.
}

Usage in components:

// Person extends ManagedModel
// HumanName extends Model, part of Person with hasOne

setup(props) {
  const manager = useModelManager(Person, () => props.id); // Internally use pinia-orm.

  // Internally tries to restore data from backup by ManagedModel.id
  // and watches for component props.id changed to replace entity and reuse component.
  //
  // manager.hasChanges - boolean, ref. Allows to check for unsaved changes before navigate to different route.
  // manager.saveChanges(); - send data to the API
  // manager.cleanup(); - drop all data, stored for current ManagedModel.
  //
  // manager.onCreating(callback) - for set model fields, when given "props.id" is empty.
  // manager.onLoadRequested(callback) - when load from API is needed.

  return {
    model: manager.model
  }
}

[CodeDredd]

I don't know yet if i am getting it right. But do you use ...super.fields() in your child models? If not that would explain your undefined fields.
A working reproduction on stackblitz or codesandbox would be nice 🙏 . Thank you.

[Arsync]

Codesandbox reproduction (see console output after model is saved).

Child model is:

export default class Person extends ManagedModel
{
    static entity = 'persons';

    static managedEntity = 'person';

    static fields()
    {
        return {
            ...super.fields()
        };
    }

    @HasOne(() => HumanName, 'id')
    declare name: HumanName;

    @Str('')
    declare birthDate: string;
}

And saving as:

useRepo(Person).save({
  id: 't4a03k6b',
  name: { }
})

Pinia state:

human-names: Object
  data: Object
    t4a03k6b: Object
      family: ""
      given: ""
      id: "t4a03k6b"
persons: Object
  data: Object
    t4a03k6b: Object // <-- id value is known by pinia-orm
      $hasChanges: undefined
      birthDate: ""
      id: undefined // <--- but not handled by model.

[CodeDredd]

ok now i understand what you want...i try to think about an solution for this. Right now it won't work and i also don't know how to make it work even with workaround.

[CodeDredd]

@Arsync I finally spent some time and found out that it already works what you want. You just have a little mistake which i can't explain because my typescript knowledge isn't that deep yet ;-)

You need to use declare prop: string instead of prop!: string

So with that it works:

import { Model } from 'pinia-orm';

/* abstract */ class ManagedModel extends Model
{
    static managedEntity: string; // for auto-navigation purpose by convention, singular entity name.

    static fields()
    {
        return {
            id: this.string(''), // Issue: always undefined in sub-entities
            $hasChanges: this.boolean(false)  // Issue: always undefined in sub-entities
        };
    }

    declare id: string;

    declare $hasChanges: boolean;
}

export { ManagedModel };

[Arsync]

Oh, with this fix it works even without override of static fields() in subclasses. Thanks! Strange behavior of a "definite assignment assertion".