Redis 不会从缓存中检索数据

Question

我正在学习一个教程，并创建了一个 cache.js 文件，该文件采用 mongoose 查询并将其 JSON.stringify 为该查询返回的值的键。目标是缓存它，然后在 app.js 中附加 .cache() mongoose.find()

当前，如果缓存为空，我让它从数据库中执行 GET，然后将其存储在缓存中。我有一个

console.log("CACHE VALUE #2");
console.log(cacheValue1);

确保数据被存储并成功输出数据。这条线有效。但是有了这条线，

console.log("CACHE VALUE #1");
console.log(cacheValue);

cacheValue 为空。

这是为什么呢？

它将值存储在底部，而键永远不会改变，所以我不明白为什么它不会返回数据而不是 null。

所以Cache Value #1 始终为空，Cache Value #2 具有正确的数据。

控制台输出：

GRABBING FROM DB
CLIENT CONNECTION STATUS: true
Setting CACHE to True
ABOUT TO RUN A QUERY
{"$and":[{"auctionType":{"$eq":"publicAuction"}},{"auctionEndDateTime":{"$gte":1582903244869}},{"blacklistGroup":{"$ne":"5e52cca7180a7605ac94648f"}},{"startTime":{"$lte":1582903244869}}],"collection":"listings"}
CACHE VALUE #1
null
CACHE VALUE #2
(THIS IS WHERE ALL MY DATA SHOWS UP)

const mongoose = require('mongoose');
const redis = require('redis');
const util = require('util');
var env = require("dotenv").config({ path: './.env' });

const client = redis.createClient(6380, process.env.REDISCACHEHOSTNAME + '.redis.cache.windows.net', {
  auth_pass: process.env.REDISCACHEKEY,
  tls: { servername: process.env.REDISCACHEHOSTNAME + '.redis.cache.windows.net' }
});


client.get = util.promisify(client.get);


const exec = mongoose.Query.prototype.exec;

mongoose.Query.prototype.cache = function () {
  this.useCache = true;
  console.log("Setting CACHE to True")
  return this;
}

mongoose.Query
  .prototype.exec = async function () {
    if (!this.useCache) {
      console.log("GRABBING FROM DB")
      console.log("CLIENT CONNECTION STATUS: " + client.connected);

      return exec.apply(this, arguments);
    }

    console.log("ABOUT TO RUN A QUERY")
    const key = JSON.stringify(Object.assign({}, this.getQuery(), {
      collection: this.mongooseCollection.name
    }));


    //See if we have a value for 'key' in redis
    console.log(key);
    const cacheValue = await client.get(key);
    console.log("CACHE VALUE #1");
    console.log(cacheValue);
    //If we do, return that
    if (cacheValue) {
      console.log("cacheValue IS TRUE");
      const doc = JSON.parse(cacheValue);
      return Array.isArray(doc)
        ? doc.map(d => new this.model(d))
        : new this.model(doc);
    }

    //Otherwise, issue the query and store the result in redis
    const result = await exec.apply(this, arguments);

    let redisData = JSON.stringify(result);
    //stores the mongoose query result in redis



    await client.set(key, JSON.stringify(redisData)), function (err) {
      console.error(err);

    }
    const cacheValue1 = await client.get(key);
    console.log("CACHE VALUE #2");
    console.log(cacheValue1);




    return result;
  }

Answer 1

根据您链接的pastebin，您的查询使用Date.now() 作为其值。这意味着每次运行查询时，时间戳都有不同的值。

因为你的键是实际的查询，并且查询有基于Date.now()的动态值，所以你的键永远不会相同，这就是为什么你以后在缓存中找不到它们，每个查询都生成一个由于Date.now() 的动态值，唯一键。

Answer 2

我在一个最小的示例中复制了您的代码，并让它按照您的要求工作。它在第一次请求后提供来自 redis 缓存的响应。我刚刚记录了值并在您的代码中发现了一些小错误，您将很容易发现它们（使用文档调用 this.model，修复集合并删除 redis 客户端的最后一个获取）。我不认为这是缓存响应的最佳方式，因为您在每个请求中都将变量设置为 true，并且在使用缓存之前您还可以访问 mongo 和 mongoose。使用中间件可以防止所有这一切，您将带走再多一些毫秒，但它仍然不是最糟糕的方式，所以这是我的最小工作示例。

const http = require('http')
const mongoose = require('mongoose')
const redis = require('redis')
const port = 3000;
const util = require('util');

const client = redis.createClient()
client.get = util.promisify(client.get);
mongoose.connect('mongodb://localhost:27017/testdb', {useNewUrlParser: true});
const exec = mongoose.Query.prototype.exec;
  var Schema = mongoose.Schema;

  var testSchema = new Schema({
    testfield:  String, // String is shorthand for {type: String}
  });


 var Test = mongoose.model('Test', testSchema);

mongoose.Query.prototype.cache = function() {
  this.useCache = true;
  console.log("Setting CACHE to True")
  return this;
}

mongoose.Query
  .prototype.exec = async function () {
    if (!this.useCache) {
      console.log("GRABBING FROM DB")
      console.log("CLIENT CONNECTION STATUS: " + client.connected);

      return exec.apply(this, arguments);
    }

    console.log("ABOUT TO RUN A QUERY")
      console.log("Query ==", this.getQuery())
      console.log("Collection == ", this.mongooseCollection.name);
    const key = JSON.stringify(Object.assign({}, this.getQuery(), {
      collection: this.mongooseCollection.name
    }));


    //See if we have a value for 'key' in redis
    console.log("KEY FROM QUERY AND COLLECTION",key);
    const cacheValue = await client.get(key);
    console.log("CACHE VALUE #1");
    console.log(cacheValue);
    //If we do, return that
    if (cacheValue) {
      console.log("cacheValue IS TRUE");
      const doc = JSON.parse(cacheValue);
        console.log("DOC == ",doc);
      return Array.isArray(doc)
        ? doc.map(d => d)
        : doc
           // return exec( Array.isArray(doc)
       // ? doc.map(d => new this.model(d))
        //: new this.model(doc))
    }

    //Otherwise, issue the query and store the result in redis
    const result = await exec.apply(this, arguments);
   // console.log("EXEC === ", exec);
   // console.log("result from query == ", result);
    let redisData = JSON.stringify(result);
    //stores the mongoose query result in redis

    console.log("REDis data ===", redisData);

    await client.set(key, redisData, function (err) {
      console.error(err);

    })




    return result;
  }

const server = http.createServer(function(req, res) {
    if(req.url === '/'){
        Test.find({}).cache().exec().then(function( docs) {
          console.log("DOCS in response == ", docs);
          res.writeHead(200, { 'Content-Type': 'text/plain' });
          res.end(JSON.stringify(docs))
        })
    }

})


server.listen(port, function() {

    console.log(`Server listening on port ${port}`)
 })