How To Extend Models

Functional Models was created so that the ModelType could be expanded. What this means, is that every Model that gets created, might have additional functions that can be consumed down stream. An example implementation of this is with functional-models-orm. This extension package, adds database functionality like save() and delete().

A Useful Tip

This can be extremely useful for when you want to swap out ModelFactory's depending on context. For example you have one model factory for a frontend and one that handles backend. You can write the models once, and use them in both contexts, adding rich functionality to either or depending on context.

Model Factory

In order to extend a ModelType you need to create your own ModelFactory. Within that factory, it should combine the extended functions to the final model factory.

import merge from 'lodash/merge'
import {
  Model,
  ModelFactory,
  ModelOptions,
  TextProperty,
  DataDescription,
  MinimalModelDefinition,
  PrimaryKeyUuidProperty,
} from 'functional-models'

// 1. We need a type that will contain our added functions. This is useful for passing along downstream.
type MyExtendedModel = {
  /**
   * We are making it so that every model has its own unique id.
   */
  getModelId: () => string
}

// 2. Create a ModelFactory, pass in our type, which extends the implementation throughout the framework.
const CustomModel: ModelFactory<MyExtendedModel> = <
  TData extends DataDescription,
>(
  modelDefinitions: MinimalModelDefinition<TData>,
  options?: ModelOptions<TData, MyExtendedModel>
) => {
  const model = Model(modelDefinitions)

  const getModelId = () => {
    const name = model.getName()
    return `${name}-unique-name`.toLowerCase()
  }

  return merge(model, {
    getModelId,
  })
}

// 3. Lets create a data type
type User = {
  id: string
  name: string
}

// 4. Now using our custom model factory create a model.
const Users = CustomModel<User>({
  pluralName: 'Users',
  namespace: '@my-package',
  properties: {
    id: PrimaryKeyUuidProperty(),
    name: TextProperty({ required: true }),
  },
})

// 5. It has our function
const uniqueId = Users.getModelId()
console.info(uniqueId)
// @my-package/users-unique-name
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