Nest.js解决自定义启动依赖项

Question

I have this factory which resolves redis:

import {RedisClient} from "redis";

export const RedisProvider = {
    provide: 'RedisToken',
    useFactory: async () => {
        return new Promise((resolve, reject) => {
            let redisClient = new RedisClient({
                host: 'resolver_redis'
            });

            redisClient.on('ready', function () {
                resolve(redisClient);
            });
        });
    }
};

But in addition to that, i wanna check if a specific key exists in redis, and if its not i want to retrive it using microservices, but for that i need to inject the microservices "client", i wanna change it to someting like that:

import {RedisClient} from "redis";

export const RedisProvider = {
    provide: 'RedisToken',
    useFactory: async () => {
        return new Promise((resolve, reject) => {
            let redisClient = new RedisClient({
                host: 'resolver_redis'
            });

            redisClient.on('ready', async function () {

                let campaigns = await redisClient.get('campaigns');

                if ( ! campaigns) {
                    // Note: "client" is not available in this scope
                    client.send('get:campaigns').subscribe(async function (campaigns) {
                        await redisClient.set('campaigns', campaigns);
                        resolve(redisClient);
                    });
                }
                else {
                    resolve(redisClient);
                }
            });
        });
    }
};

the only problem is that i dont have access to the "client", or do i? it can also be anther provider if it makes more sense, but then i will also need priority for loading the providers, i am doing this because the application requires this data for startup stuff

Answer 1

I don't recommend adding more logic in providers factory, since it could be more controlled in the consumer of this provider ie: the services

in your services code you could do something like this

import { Component, Inject, OnModuleInit } from '@nestjs/common';
...
@Component()
export class MyService implements OnModuleInit {
    constructor(@Inject(REDIS_TOKEN) private readonly redis: RedisClient) {}
    onModuleInit() {
            const campaigns = await this.redis.get('campaigns');
            ...
    }
}

I assume that REDIS_TOKEN is constant saved on constants.ts file and equal to RedisToken .

this will be more controlled. the code of checking for the campaigns key will be executed once your Module init.

for more information about Module Lifecycle checkout: Modules Lifecycle