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'use strict';
const mongoose = require('mongoose');const redis = require('redis');
// setting up redis serverconst client = redis.createClient();client.connect().then();const exec = mongoose.Query.prototype.exec;
mongoose.Query.prototype.cache = function(options = {}) {  this.useCache = true;  // setting up primary user key  this.hashKey = JSON.stringify(options.key || '');  return this;};
mongoose.Query.prototype.exec = async function() {  if (!this.useCache) return exec.apply(this, arguments);
  // setting up query key  const key = JSON.stringify(Object.assign({},    this.getQuery(), { collection: this.mongooseCollection.name })  );
  // looking for cache  const cacheData = await client.hGet(this.hashKey, key).catch((err) => console.log(err));  if (cacheData) {    console.log('from redis');    const doc = JSON.parse(cacheData);    // inserting doc to make as actual mongodb query    return Array.isArray(doc) ? doc.map(d => new this.model(d)) : new this.model(doc);  }
  const result = await exec.apply(this, arguments);  client.hSet(this.hashKey, key, JSON.stringify(result));  return result;};
module.exports = {  clearCache(hashKey) {    client.del(JSON.stringify(hashKey));  }};