nestjs-ioc-example-1

drink.model.ts

export interface Drink {
    name: string;
    alcoholByVolume: number;
}

drink.module.ts

import { Module } from '@nestjs/common';

import { DrinkService } from './drink.service';

@Module({
    providers: [
        DrinkService,
    ],
    exports: [
        DrinkService,
    ],
})
export class DrinkModule {}

drink.provider.ts

import { Drink } from './drink.model';

export interface DrinkProvider {
    getDrinks(): Promise<Drink[]>;
}

drink.service.ts

import { Injectable } from '@nestjs/common';

import { Drink } from './drink.model';
import { DrinkProvider } from './drink.provider';

@Injectable()
export class DrinkService {

    private readonly providers: DrinkProvider[] = [];

    registerProvider(provider: DrinkProvider): void {
        this.providers.push(provider);
    }

    async getDrinks(): Promise<Drink[]> {
        const drinks: Drink[] = [];

        for (const provider of this.providers) {
            drinks.push(...await provider.getDrinks());
        }

        return drinks;
    }
}

spirit.drink.provider.ts

import { Injectable } from '@nestjs/common';

import { DrinkProvider } from '../drink.provider';
import { Drink } from '../drink.model';
import { DrinkService } from '../drink.service';

@Injectable()
export class SpiritDrinkProvider implements DrinkProvider {

    // This is the weird part that we'll improve
    constructor(
        drinkService: DrinkService,
    ) {
        drinkService.registerProvider(this);
    }

    public getDrinks(): Promise<Drink[]> {
        return Promise.resolve([
            {
                name: 'Rum',
                alcoholByVolume: 45,
            },
            {
                name: 'Arrack',
                alcoholByVolume: 50,
            },
            {
                name: 'Cognac',
                alcoholByVolume: 40,
            },
        ]);
    }
}

spirit.module.ts

import { Module } from '@nestjs/common';

import { DrinkModule } from '../drink.module';
import { SpiritDrinkProvider } from './spirit.drink.provider';

@Module({
    imports: [
        DrinkModule,
    ],
    providers: [
        SpiritDrinkProvider,
    ],
})
export class SpiritModule {}