Composing models

What you'll learn

• Creating composables to share features across some of your models
• Creating your own model factory with predefined features for all of your models

Sometimes, you may want to share common features across your models. To solve this, you may use one of the two solutions proposed by Foscia:

• Composition, to share features across some of your models
• Factory, to share features across all of your models

Composition

When you need to share features across some of your models, you should use composition.

The first step is to create a composable with the features you want to share. This is done through makeComposable and uses the same syntax as makeModel.

The created composable will get its custom properties (e.g. published below) rewritten to protect their descriptor. This allows using spread syntax when using composable in other models' definition.

composables/publishable.js

import { attr, makeComposable, toDate } from 'foscia/core';

export default makeComposable({
    publishedAt: attr(toDate()),
    get published() {
        return !!this.publishedAt;
    },
});

The easiest way to use your composable is to object-spread it inside your model's definition.

models/post.js

import { makeModel } from 'foscia/core';
import publishable from '../composables/publishable';

export default class Post extends makeModel('posts', {
    ...publishable,
    /** post definition */
}) {}

You may also use the model extends method as follows:

models/post.js

import { makeModel } from 'foscia/core';
import publishable from '../composables/publishable';

export default class Post extends makeModel('posts').extends(publishable) {}

caution

Please note that when using the object spread syntax, you won't be able to get a correctly typed this context inside the current definition object (it is still available in next/previous definition or in class body). This is because of an issue due to a TypeScript limitation.

Factory

When you need to share features across all of your models, you should use a custom model factory. It will replace the Foscia's makeModel function.

makeModel.js

import { attr, makeModelFactory, toDate } from 'foscia/core';

export default makeModelFactory(
    {
        createdAt: attr(toDate()),
        updatedAt: attr(toDate()),
        get wasChangedSinceCreation() {
            return this.createdAt.getTime() === this.updatedAt.getTime();
        },
    },
    {
        /* base configuration */
    },
);

Once your factory is ready, you can use in replacement of the classical makeModel, as it will have the same features.

import makeModel from './makeModel';

export default class Post extends makeModel('posts', {
    /* definition */
}) {}