我想要实现的目标:我想创建一辆必须与其经销商有正确映射的汽车，然后将这辆车存储在列表/数组中我的公司文档存在于 myKaarma 数据库中的公司集合中。
我面临的问题:所有逻辑都是正确的，但问题是由于异步性质而产生的，即使我正在使用回调。 我知道这个问题，但不知道如何解决。
让我解释一下问题是什么:
我使用 Mongoose 的公司模型:
// jshint node :true
"use strict";
const MONGOOSE = require("mongoose"),
DB = MONGOOSE.connection;
let companySchema = MONGOOSE.Schema({
company_name: {
type: String, required: true
},
company_location: {
type: String, require: true
},
cars: [{
model: {
type: String,required: true
},
year: {
type: Number, required: true
},
PriceInINR: {
type: Number, required: true
},
trim: {
type: String, required: true
},
engine: {
type: String, required: true
},
body: {
type: String, required: true
},
color: {
type: String, required: true
},
transmission_type: {
type: String, required: true
},
dealer_id: {
type: String, required: true
}
}]
});
let collection_name = "companies";
let CompanyModel = MONGOOSE.model(collection_name, companySchema);
createAscendingIndex_on_company_name(DB);
module.exports = CompanyModel;
// indexing at schema level --> using node js
function createAscendingIndex_on_company_name(DB, callback) {
let collection = DB.collection(collection_name);
// ? Create the index
collection.createIndex({
company_name: 1, // specifies : indexing type is ascending indexing
}, {
unique: true
}, function (err, result) {
if (err) {
console.log("error while setting up indexing on companies collection");
}
console.log("index created ", result, "<<<<<<<<", collection_name, " collection");
// callback("result");
});
}
//? NOTE : Creating indexes in MongoDB is an idempotent operation. So running db.names.createIndex({name:1}) would create the index only if it didn't already exist.
您会注意到，我已建立索引并将 company_name 设置为唯一，因此那里不能有重复的条目这就是问题
在我的代码中，当我这样做时: //?检查公司是否存在:如果不存在，则创建一个，我遇到的问题是，因为nodejs是异步的并且速度非常快:[所以假设我有5条汽车记录]所以所有这五辆车实际上进入了我检查的代码:
CompanyModel.find({
company_name: company_name
}, (err, companies) => {.....}
而且速度如此之快，就像所有的公司同时进行一样，当然，公司文档中目前不存在任何这样的公司，所以它们都通过了 if 条件
if (companies.length === 0) {...});
现在，在我的记录中，有 3 辆同一家公司的汽车，它们几乎同时进入，并且都同时再次通过这些条件，但一旦它们通过上述条件，我就会要求 Mongo 创建公司文档
let company = new CompanyModel({
company_name: company_name,
company_location: company_location,
cars: [car]
});
company.save((err) => {...}
但是现在，所有 3 条记录都在这里创建一个新的公司对象并添加到集合中。但是一旦其中一个创建了文档并添加到集合中，同时另外两个也创建了他们的对象，但现在由于已经创建并添加了一个对象，所以 Mongo 会在这里抛出独特的异常。
我想要发生的事情是，当我们发现一个重复的对象时，那么同一家公司的新车应该被插入公司文档的数组中，该数组的字段为 cars
注意:这种情况仅适用于公司不在集合中的情况，但如果它已经存在，那么我的代码工作正常，它成功地将所有汽车插入集合中。各自公司的cars字段。
这是正在做我想做的事情的函数:
function map_and_save_cars_in_garage() {
let carList = require("./test.json");
let totalCar = carList.length;
console.log(carList);
carList.forEach((carRecord, index) => {
let company_name = carRecord.make.toLowerCase();
let company_location = "USA";
// build a car
let car = {
model: carRecord.model,
year: carRecord.year,
PriceInINR: carRecord.priceInr,
trim: carRecord.trim,
engine: carRecord.engine,
body: carRecord.body,
color: carRecord.color,
transmission_type: carRecord.transmission,
dealer_id: undefined, // --> just for now
};
// ? search for the correct dealer --> for mapping
let dealer_email = "bitBattle_2018_" + carRecord.DealerID + "_@myKarmaa.com";
DealerModel.find({
email: dealer_email
}, (err, dealer) => {
if (err) {
console.log("Error : dealer not found for this car");
throw new Error(err);
}
car.dealer_id = dealer[0]._id; // ? update the dealer_id
// ? check if the company exists : and if not then create one
CompanyModel.find({
company_name: company_name
}, (err, companies) => {
if (err) {
console.log("Error : while finding the compay");
throw new Error(err);
}
console.log(company_name, companies);
if (companies.length === 0) {
console.log("No such Company car exists in the garrage --> creating one");
let company = new CompanyModel({
company_name: company_name,
company_location: company_location,
cars: [car]
});
company.save((err) => {
if (err) {
console.log("Error : while adding company ");
throw new Error(err);
}
console.log(index, "<<<<<<<< INDEX ", totalCar);
if (index === totalCar - 1) {
console.log("done");
res.send("build complete");
// build_complete();
}
});
} else {
console.log("Company already exists in garage : add this car with all other cars of this company");
let company = companies[0]; // ? as its sure that they are unique
let query = {
_id: company._id
};
let updat_command = {
$push: {
cars: car
}
};
CompanyModel.updateOne(query, updat_command, (err) => {
if (err) {
console.log("Error : while pushing car to the compay's cars");
throw new Error(err);
}
console.log(index, "<<<<<<<< INDEX ", totalCar);
if (index === totalCar - 1) {
console.log("done");
res.send("build complete");
// build_complete();
}
});
}
});
});
console.log(index, "<<<<<<<< INDEX--OUTER ", totalCar);
});
}
输出:
[nodemon] restarting due to changes...
[nodemon] starting `node app.js`
[[20:39:12.519]] [LOG] server live
[[20:39:12.626]] [LOG] Connected to DB : SUCCESS
[[20:39:12.642]] [LOG] index created email_1 <<<<<<<< buyers collection
[[20:39:12.647]] [LOG] index created email_1 <<<<<<<< dealers collection
[[20:39:12.795]] [LOG] index created company_name_1 <<<<<<<< companies collection
[[20:39:42.081]] [LOG] start saving cars
[[20:39:42.084]] [LOG] [ { id: '2',
vin: '5GAKRBKD9EJ323900',
make: 'Buick',
model: 'ENCLAVE',
year: '2014',
priceInr: '2537993',
trim: 'Leather FWD',
engine: 'SPORT UTILITY 4-DR',
body: '3.6L V6 DOHC 24V',
color: 'Silver',
transmission: 'Manual',
DealerID: '103' },
{ id: '4',
vin: '2GKALSEKXD6184074',
make: 'GMC',
model: 'TERRAIN',
year: '2013',
priceInr: '3851710',
trim: 'SLE2 FWD',
engine: 'SPORT UTILITY 4-DR',
body: '2.4L L4 DOHC 16V FFV',
color: 'Yellow',
transmission: 'Manual',
DealerID: '103' },
{ id: '6',
vin: '1GC1KXE86EF127166',
make: 'Chevrolet',
model: 'SILVERADO 2500HD',
year: '2014',
priceInr: '840547',
trim: 'LT Crew Cab 4WD',
engine: 'CREW CAB PICKUP 4-DR',
body: '6.6L V8 OHV 32V TURBO DIESEL',
color: 'Grey',
transmission: 'Automatic',
DealerID: '103' },
{ id: '8',
vin: '1GKKRTED1CJ211299',
make: 'GMC',
model: 'Acadia',
year: '2012',
priceInr: '3805008',
trim: 'Denali FWD',
engine: 'SPORT UTILITY 4-DR',
body: '3.6L V6 DOHC 24V',
color: 'Metallic White',
transmission: 'Automatic',
DealerID: '103' },
{ id: '10',
vin: '1GKKVTKD9EJ282303',
make: 'GMC',
model: 'ACADIA',
year: '2014',
priceInr: '1730235',
trim: 'Denali AWD',
engine: 'SPORT UTILITY 4-DR',
body: '3.6L V6 DOHC 24V',
color: 'Black',
transmission: 'Manual',
DealerID: '103' },
{ id: '12',
vin: '1GKS1AKC0FR200193',
make: 'GMC',
model: 'YUKON',
year: '2015',
priceInr: '3129397',
trim: 'SLE 2WD',
engine: 'SPORT UTILITY 4-DR',
body: '5.3L V8 OHV 16V',
color: 'Silver',
transmission: 'Manual',
DealerID: '103' } ]
[[20:39:42.089]] [LOG] 0 '<<<<<<<< INDEX--OUTER ' 6
[[20:39:42.089]] [LOG] 1 '<<<<<<<< INDEX--OUTER ' 6
[[20:39:42.090]] [LOG] 2 '<<<<<<<< INDEX--OUTER ' 6
[[20:39:42.090]] [LOG] 3 '<<<<<<<< INDEX--OUTER ' 6
[[20:39:42.090]] [LOG] 4 '<<<<<<<< INDEX--OUTER ' 6
[[20:39:42.090]] [LOG] 5 '<<<<<<<< INDEX--OUTER ' 6
[[20:39:42.120]] [LOG] gmc []
[[20:39:42.120]] [LOG] No such Company car exists in the garrage --> creating one
[[20:39:42.134]] [LOG] buick []
[[20:39:42.134]] [LOG] No such Company car exists in the garrage --> creating one
[[20:39:42.138]] [LOG] gmc []
[[20:39:42.138]] [LOG] No such Company car exists in the garrage --> creating one
[[20:39:42.143]] [LOG] chevrolet []
[[20:39:42.143]] [LOG] No such Company car exists in the garrage --> creating one
[[20:39:42.146]] [LOG] gmc []
[[20:39:42.146]] [LOG] No such Company car exists in the garrage --> creating one
[[20:39:42.150]] [LOG] 1 '<<<<<<<< INDEX ' 6
[[20:39:42.150]] [LOG] gmc []
[[20:39:42.151]] [LOG] No such Company car exists in the garrage --> creating one
[[20:39:42.153]] [LOG] 0 '<<<<<<<< INDEX ' 6
[[20:39:42.154]] [LOG] Error : while adding company
events.js:183
throw er; // Unhandled 'error' event
^
Error: MongoError: E11000 duplicate key error collection: myKaarma.companies index: company_name_1 dup key: { : "gmc" }
at company.save (/Users/prashant/Desktop/appathon/route/api.js:179:55)
at /Users/prashant/Desktop/appathon/node_modules/mongoose/lib/model.js:4437:16
at $__save.error (/Users/prashant/Desktop/appathon/node_modules/mongoose/lib/model.js:397:16)
at /Users/prashant/Desktop/appathon/node_modules/kareem/index.js:246:48
at next (/Users/prashant/Desktop/appathon/node_modules/kareem/index.js:167:27)
at next (/Users/prashant/Desktop/appathon/node_modules/kareem/index.js:169:9)
at Kareem.execPost (/Users/prashant/Desktop/appathon/node_modules/kareem/index.js:217:3)
at _handleWrapError (/Users/prashant/Desktop/appathon/node_modules/kareem/index.js:245:21)
at _cb (/Users/prashant/Desktop/appathon/node_modules/kareem/index.js:304:16)
at /Users/prashant/Desktop/appathon/node_modules/mongoose/lib/model.js:258:9
at /Users/prashant/Desktop/appathon/node_modules/kareem/index.js:135:16
at _combinedTickCallback (internal/process/next_tick.js:131:7)
at process._tickCallback (internal/process/next_tick.js:180:9)
我怎样才能摆脱这个困境？
最佳答案
如果您使用的 Node 高于 Node 7(我希望如此......)，您可以使用 async/await 使此代码更易于处理。您还可以使用 mongoose 中的 findOne，这样您就不必处理数组，因为您知道每个结果只有一个。
此代码工作的技巧是，它会等到前一辆车插入数据库后再插入另一辆车。
async function map_and_save_cars_in_garage() {
let carList = require("./test.json");
let totalCar = carList.length;
for (let carRecord of carList) {
let company_name = carRecord.make.toLowerCase();
let company_location = "USA";
// build a car
let car = {
model: carRecord.model,
year: carRecord.year,
PriceInINR: carRecord.priceInr,
trim: carRecord.trim,
engine: carRecord.engine,
body: carRecord.body,
color: carRecord.color,
transmission_type: carRecord.transmission,
dealer_id: undefined, // --> just for now
};
let dealer_email = "bitBattle_2018_" + carRecord.DealerID + "_@myKarmaa.com";
try {
let dealer = await DealerModel.findOne({
email: dealer_email
}).exec();
car.dealer_id = dealer._id;
let company = await CompanyModel.findOne({
company_name: company_name
}).exec();
if (!company) {
console.log("No such Company car exists in the garrage --> creating one");
let company = new CompanyModel({
company_name: company_name,
company_location: company_location,
cars: [car]
});
await company.save();
} else {
console.log("Company already exists in garage : add this car with all other cars of this company");
await CompanyModel.updateOne({
_id: company._id
}, {
$push: {
cars: car
}
}).exec();
}
} catch (err) {
throw new Error(err);
}
}
console.log("done");
res.send("build complete");
}
我可能尝试的另一件事是不等待创建每辆车，而是创建一个数组(与数据库相比，它将立即访问)，其中包含新插入的公司，如下所示:
async function map_and_save_cars_in_garage() {
let carList = require("./test.json");
let totalCar = carList.length;
let newCompanies = {};
for (let carRecord of carList) {
(async function () {
let company_name = carRecord.make.toLowerCase();
let company_location = "USA";
// build a car
let car = {
model: carRecord.model,
year: carRecord.year,
PriceInINR: carRecord.priceInr,
trim: carRecord.trim,
engine: carRecord.engine,
body: carRecord.body,
color: carRecord.color,
transmission_type: carRecord.transmission,
dealer_id: undefined, // --> just for now
};
let dealer_email = "bitBattle_2018_" + carRecord.DealerID + "_@myKarmaa.com";
try {
let dealer = await DealerModel.findOne({
email: dealer_email
}).exec();
car.dealer_id = dealer._id;
// Check for company in newCompanies
let company = newCompanies[company_name];
// If company is not in newcompanies it will be undefined so this if statement will be executed
if (!company) {
// If company is not found in database this will be null
await CompanyModel.findOne({
company_name: company_name
}).exec();
}
// If company is null then create a new one
if (!company) {
console.log("No such Company car exists in the garrage --> creating one");
let company = new CompanyModel({
company_name: company_name,
company_location: company_location,
cars: [car]
});
// Add company to newCompanies
newCompanies[company_name] = company;
await company.save();
} else {
console.log("Company already exists in garage : add this car with all other cars of this company");
await CompanyModel.updateOne({
_id: company._id
}, {
$push: {
cars: car
}
}).exec();
}
} catch (err) {
throw new Error(err);
}
})();
}
console.log("done");
res.send("build complete");
}
这不必等待以前的汽车被添加到数据库中。
关于javascript - Mongo 陷阱 : how can I perform kind of synchronously, 上的异步操作我有正确的逻辑，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/52170275/