@loopback/repository/src/define-model-class.ts

// Copyright IBM Corp. and LoopBack contributors 2019,2020. All Rights Reserved.
// Node module: @loopback/repository
// This file is licensed under the MIT License.
// License text available at https://opensource.org/licenses/MIT

import * as assert from 'assert';
import {DataObject, PrototypeOf} from './common-types';
import {model} from './decorators';
import {Model, ModelDefinition} from './model';

/**
 * Create (define) a new model class with the given name and definition.
 *
 * @remarks
 *
 * ```ts
 * const Product = defineModelClass(Entity, new ModelDefinition('Product'));
 * ```
 *
 * To enable type safety, you should describe properties of your model:
 *
 * ```ts
 * const Product = defineModelClass<
 *  typeof Entity,
 *  {id: number, name: string}
 * >(Entity, new ModelDefinition('Product'));
 * ```
 *
 * If your model allows arbitrary (free-form) properties, then add `AnyObject`
 * to the type describing model properties.
 *
 * ```ts
 * const Product = defineModelClass<
 *  typeof Entity,
 *  AnyObject & {id: number},
 * >(Entity, new ModelDefinition('Product'));
 * ```
 *
 * @param base The base model to extend, typically Model or Entity.
 *  You can also use your own base class, e.g. `User`.
 * @param definition Definition of the model to create.
 * @typeParam BaseCtor Constructor type of the base class,
 *   e.g `typeof Model` or `typeof Entity`
 * @typeParam Props Interface describing model properties,
 *   e.g. `{title: string}` or `AnyObject & {id: number}`.
 */
export function defineModelClass<
  BaseCtor extends typeof Model,
  Props extends object = {},
>(
  base: BaseCtor /* Model or Entity */,
  definition: ModelDefinition,
): DynamicModelCtor<BaseCtor, Props> {
  const modelName = definition.name;
  const defineNamedModelClass = new Function(
    base.name,
    `return class ${modelName} extends ${base.name} {}`,
  );
  const modelClass = defineNamedModelClass(base) as DynamicModelCtor<
    BaseCtor,
    Props
  >;
  assert.equal(modelClass.name, modelName);

  // Apply `@model(definition)` to the generated class
  model(definition)(modelClass);
  return modelClass;
}

/**
 * A type describing a model class created via `defineModelClass`.
 *
 * Assuming template arguments `BaseCtor` and `Props`, this type describes
 * a class constructor with the following properties:
 * - a constructor function accepting `DataObject<Props>` as the only argument,
 *   this argument is optional
 * - all static fields (properties, methods) from `BaseCtor` are inherited and
 *   available as static fields on the dynamic class
 * - all prototype fields from `BaseCtor` prototype are inherited and available
 *   as prototype fields on the dynamic class
 */
export type DynamicModelCtor<
  BaseCtor extends typeof Model,
  Props extends object,
> = {
  /** Model constructor accepting partial model data. */
  new (
    data?: DataObject<PrototypeOf<BaseCtor> & Props>,
  ): PrototypeOf<BaseCtor> & Props;
} & BaseCtor;