redis不会从缓存中检索数据

9o685dep  于 2021-06-09  发布在  Redis
关注(0)|答案(2)|浏览(377)

我遵循一个教程,创建了一个cache.js文件,该文件接受mongoose查询,json.stringifies将其放入该查询返回的值的键中。目标是缓存它,然后附加 .cache() 在app.js中 mongoose.find()
如果缓存是空的,我让它从数据库中获取数据,然后将其存储在缓存中。我有一个

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

这样可以确保数据得到存储并成功输出数据。这条线行得通。但有了这条线,

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

这个 cacheValue 为空。
为什么?
它存储在底部的值和键从来没有改变,所以我不明白为什么它不会返回数据而不是null。
所以呢 Cache Value #1 始终为空且 Cache Value #2 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;
  }
9rbhqvlz

9rbhqvlz1#

我在一个很小的例子中复制了你的代码,我让它按照你的要求工作。它在第一个请求之后服务于redis缓存的响应。我刚刚记录了一些值并在代码中发现了一些小错误,您将很容易发现它们(用doc调用this.model,修复集合并删除redis客户端的最后一个get)。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一个变量设置为true,并且在使用缓存之前访问mongo和mongoose。通过中间件,所有这些都可以避免,您将带走更多ms,但这仍然不是最坏的方式,因此这里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}`)
 })
ssgvzors

ssgvzors2#

根据您链接的粘贴箱,您的查询将使用 Date.now() 他们的价值观。这意味着每次运行查询时,时间戳的值都不同。
因为您的键是实际的查询,并且查询具有基于 Date.now() ,您的键将永远不会相同,这就是为什么以后在缓存中找不到它们的原因,每个查询都会生成一个唯一的键,因为 Date.now() .

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