(Conceptual - using a theoretical caching service wrapper)

 // Assuming a custom caching service
  import { Injectable, Inject } from '@nestjs/common';
  import { CACHE_MANAGER } from '@nestjs/cache-manager';
  import { Cache } from 'cache-manager';

  @Injectable()
  export class CustomCacheService {
    constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}

    async get(key: string, ttl: number = null): Promise<any> {
        return await this.cacheManager.get(key);
    }

    async set(key: string, value: any, ttl: number = null): Promise<void> {
        if(ttl){
            await this.cacheManager.set(key, value, ttl);
        } else {
            await this.cacheManager.set(key, value);
        }
    }
  }

  // In your controller or service
  async getUserProfile(userId: string) {
    const cacheKey = `user:${userId}`;
    let userProfile = await this.customCacheService.get(cacheKey);

    if (!userProfile) {
      userProfile = await this.userService.getUserProfile(userId);
      await this.customCacheService.set(cacheKey, userProfile, { ttl: 300 }); // 5 minutes (300 seconds)
    }

    return userProfile;
  }

  async getProductDetails(productId: string) {
    const cacheKey = `product:${productId}`;
    let productDetails = await this.customCacheService.get(cacheKey);

    if (!productDetails) {
      productDetails = await this.productService.getProductDetails(productId);
      await this.customCacheService.set(cacheKey, productDetails, { ttl: 3600 }); // 1 hour (3600 seconds)
    }

    return productDetails;
  } 

Explanation:

• This example uses a CustomCacheService to abstract the caching logic. This would interact with the CACHE_MANAGER in NestJS, likely using Redis or Memcached.
• The getUserProfile and getProductDetails functions demonstrate setting different TTLs (ttl option) for different types of data. User profiles have a shorter TTL (5 minutes), while product details have a longer TTL (1 hour).
• Note: The exact syntax for setting TTLs might vary slightly depending on the underlying cache provider (e.g., Redis, Memcached). The provided example shows the general principle.

(Conceptual - showing Redis Pub/Sub integration)

 // Assume a Redis client is already configured and injected

  // Publisher (e.g., in your data update service)
  async updateProduct(productId: string, productData: any) {
    // Update product in the database
    await this.productRepository.update(productId, productData);

    // Publish a message to the 'productUpdates' channel
    this.redisClient.publish('productUpdates', productId); // Publish the product ID
  }


  // Subscriber (e.g., in your caching service)
  async onModuleInit() {
    const subscriber = this.redisClient.duplicate(); // Create a separate connection for subscribing

    subscriber.subscribe('productUpdates', (productId) => {
      // Invalidate the cache for the updated product
      this.cacheManager.del(`product:${productId}`);
      console.log(`Cache invalidated for product: ${productId}`);
    });
  } 

Explanation:

• The updateProduct function updates the product in the database and then publishes a message containing the product ID to the productUpdates channel.
• The onModuleInit method in a service (likely your caching service) subscribes to the productUpdates channel.
• When a message is received, the subscriber extracts the product ID and invalidates the corresponding cache entry using this.cacheManager.del().
• You need to have a Redis client properly setup in your NestJS application, injected as a dependency.

(Conceptual - showing in-memory and Redis caching)

 import { Injectable, Inject } from '@nestjs/common';
  import { CACHE_MANAGER } from '@nestjs/cache-manager';
  import { Cache } from 'cache-manager';

  @Injectable()
  export class ProductService {
    constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}

    async getProductDetails(productId: string): Promise<any> {
      // 1. Check in-memory cache (fastest)
      const inMemoryCacheKey = `product:in-memory:${productId}`;
      let productDetails = await this.cacheManager.get(inMemoryCacheKey);

      if (!productDetails) {
        // 2. Check Redis cache (slower than in-memory, but distributed)
        const redisCacheKey = `product:redis:${productId}`;
        productDetails = await this.cacheManager.get(redisCacheKey);

        if (!productDetails) {
          // 3. Fetch from database (slowest)
          productDetails = await this.productRepository.findById(productId);

          // 4. Store in both Redis and in-memory caches
          await this.cacheManager.set(redisCacheKey, productDetails, { ttl: 3600 }); // Redis TTL
          await this.cacheManager.set(inMemoryCacheKey, productDetails, { ttl: 60 });  // In-memory TTL (shorter)
        } else {
            //Store in memory since it came from Redis
            await this.cacheManager.set(inMemoryCacheKey, productDetails, { ttl: 60 });
        }
      }


      return productDetails;
    }
  } 

Explanation:

• The getProductDetails function first checks the in-memory cache. If the data is found there, it's returned immediately.
• If the data is not in the in-memory cache, it checks the Redis cache.
• If the data is not in either cache, it's fetched from the database.
• Finally, the data is stored in both the Redis cache (with a longer TTL) and the in-memory cache (with a shorter TTL) for future requests.
• In this scenario, the CACHE_MANAGER would likely be configured to use both an in-memory store and a Redis store (or Memcached). You'd configure the `CacheModule` in your app.module.ts to use the two stores.