问题
I'm following a tutorial and I created a cache.js file that takes the mongoose query and JSON.stringifies it into the key for the values being returned by that query. The goal is to cache that and then append .cache() inside app.js where the mongoose.find() is
Currenty if the cache is empty, I have it do a GET from the DB and then store it in the cache. I have a
console.log("CACHE VALUE #2");
console.log(cacheValue1);
that ensures that the data is getting stored and outputs the data successfully. This line works. But with this line,
console.log("CACHE VALUE #1");
console.log(cacheValue);
the cacheValue is null.
Why is that?
It stores at the bottom the value and the key never changes so I don't understand why it won't return the data instead of null.
So Cache Value #1 is always null and Cache Value #2 has the correct data.
CONSOLE OUTPUT:
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;
}
回答1:
Based on the pastebin you linked, your queries are using Date.now() for their values. This means that each time a query is run, you have different values for the timestamp.
Because your keys are the actual query, and the query has dynamic values based on Date.now(), your keys will never be the same, which is why you can't find them in the cache later, each query is generating a unique key because of the dynamic values of Date.now().
回答2:
I reproduced your code within a minimal example and I got it working as you wanted.It serves the response from the redis cache after the first request. I just logged values and found some small mistakes in your code,you will easily spot them(calling this.model with the doc, fix the set and remove the last get for the redis client). I don't think that this is the best way to cache responses because you set a variable to true in every request and also you reach to mongo and mongoose before you use cache.With a middleware all this can be prevented and you will take away some more ms but still its not the worst way either so here is my minimal working example.
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}`)
})
来源：https://stackoverflow.com/questions/60380902/redis-wont-retrieve-data-from-cache