Question

我正在Node.js中创建我的第一个应用程序，它应该按顺序执行这些操作：

连接到PostgreSQL数据库
创建一个表（如果它已存在，做任何事情）
对两个网站进行网页抓取并保存有关db
使用D3.js和数据库上的数据创建可视化
它与数据库断开连接。

我发布了有关插入操作的previous question。现在问题是async / await。

我知道Node.js是异步的，而我应该同步执行操作。我正在使用Node.js v8.9.4，所以我使用async / await构造。

我读了一下'async / await如何，但我觉得很难正确使用它。

这是我的应用程序的方案（ app.js 文件）：

const postgreSQLlib = require('./middlewares/postgreSQLlib.js')
const scraperCovIt = require('./routers/scraperCovIt.js');
const scraperCov = require('./routers/scraperCov.js');

const start = async function() {
    // STEP 0 - Start
    await console.log('\nSTART');

    // STEP 1 - Connect to db
    await postgreSQLlib.connect();

    // STEP 2 - Create tables
    var queryCreateCoverages = {
        text: 'CREATE TABLE IF NOT EXISTS coverages ('+
                    'id SERIAL PRIMARY KEY,' +
                    'vaccine VARCHAR(64) NOT NULL,' + 
                    'country VARCHAR(255) NOT NULL,' +
                    'region VARCHAR(255),' +
                    'year VARCHAR(4) NOT NULL,' +
                    'value VARCHAR(12) NOT NULL);'
    };
    var queryRes = await postgreSQLlib.query(queryCreateCoverages, '[CREATE TABLE coverages]');

    // STEP 3 - Get data
    await scraperCovIt.download();
    await scraperCov.download();

    // STEP 4 - Disconnect from db
    await postgreSQLlib.disconnect();

    // STEP 5 - End
    return '\nFINISH';
}

// start application
start()
.then(function(res) {
    console.log(res);
})
.catch(function(err) {
    console.log(err);
});

postgreSQLlib.js ：

const {Client} = require('pg'); 
const connectionString = 'postgres://admin:admin@localhost:5432/db';
let client;
var methods = {};

methods.connect = async function() {
    client = new Client({connectionString});
    return await client.connect()
    .then(async function() {
        await console.log('\nConnected to ' + client.database + ' at ' + client.host + ':' + client.port + ' as ' + client.user + ' (pass: ' + client.password + ')');
    })
    .catch(function(err) {
        console.log('\nError during connection to PostgreSQL');
        throw err;
    });
}

methods.query = async function(query, print) {
    return await client.query(query)
    .then(function(res) {
        console.log(print, 'OK query');
        return res;
    })
    .catch(function(err) { 
        console.log(print, 'ERR query');
    });
}

methods.disconnect = async function() {
    return await client.end()
    .then(function() {
        console.log('\nConnection has ended');
    })
    .catch(function(err) {
        console.log('\nError during clossing connection');
        throw err;
    }); 
}

module.exports = methods;

scraperCov.js ：

var cheerio = require('cheerio');
var request = require('request-promise');
var postgreSQLlib = require('../middlewares/postgreSQLlib.js');

var methods = {};

var countries = {
    'Albania': 'ALB',
    'Austria': 'AUT',
    'Belgium': 'BEL'
};

methods.download = async function(req, res) {
    for(country in countries) {
        console.log('\nCOUNTRY:', country);
        var url = 'http://apps.who.int/immunization_monitoring/globalsummary/coverages?c=' + countries[country];
        let res = await request(url);
        insert(res);
    }
}

module.exports = methods;

let insert = async function(html) {
    $ = cheerio.load(html);

    var years = [];
    var vaccines = [];
    var coverages = [];

    $('.ts .year').each(function() {
        years.push($(this).text().trim());
    });
    $('.ts .odd td a, .ts .even td a').each(function() {
        vaccines.push($(this).text().trim());
    });
    $('.ts .odd .statistics_small, .ts .even .statistics_small').each(function() {
        coverages.push($(this).text().trim());
    });

    const numYears = years.length;
    const numVaccines = vaccines.length;
    for(var vaccineIdx = 0; vaccineIdx < numVaccines; vaccineIdx++) {
        for(var yearIdx = 0; yearIdx < numYears; yearIdx++) {
            let obj = {
                year: years[yearIdx],
                country: country,
                region: '',
                vaccine: vaccines[vaccineIdx],
                coverage: coverages[vaccineIdx*numYears + yearIdx]
           }

            // save on db
            const queryInsert = {
                text: 'INSERT INTO coverages (vaccine, country, region, year, value) VALUES ($1, $2, $3, $4, $5);',
                values: [vaccines[vaccineIdx], country, '', years[yearIdx], coverages[vaccineIdx*numYears + yearIdx]]
            }
            var printText = '[INSERT ' + country + ' IN coverages]';
            var queryRes = await postgreSQLlib.query(queryInsert, printText);
        }
    }
}

scraperCovIt.js ：

var textract = require('textract');
var postgreSQLlib = require('../middlewares/postgreSQLlib.js');

var methods = {};
var jsons = [];
var mainUrl = 'http://www.salute.gov.it/portale/documentazione/p6_2_8_3_1.jsp?id=20';
var urls = [ 
    {year: '2013', link: 'http://www.salute.gov.it/imgs/C_17_tavole_20_allegati_iitemAllegati_0_fileAllegati_itemFile_1_file.pdf'}, 
    {year: '2012', link: 'http://www.salute.gov.it/imgs/C_17_tavole_20_allegati_iitemAllegati_5_fileAllegati_itemFile_0_file.pdf'}, 
    {year: '2011', link: 'http://www.salute.gov.it/imgs/C_17_tavole_20_allegati_iitemAllegati_6_fileAllegati_itemFile_0_file.pdf'}
];

methods.download = async function(req, res) {
    await extractText();
}

async function extractText() {
    var config = {
        preserveLineBreaks: true
    };
    urls.forEach(function(url) {
        textract.fromUrl(url.link, config, async function(error, text) {
            if(error) {
                throw error;
            }
            switch(url.year) {
                case '2011': 
                case '2012':
                    await extractTextType1(url, text);
                    break;
                case '2013': 
                    await extractTextType2(url, text);
                    break;
                default:
                    await console.log('Error: no case');
            }
        });
    });
}

async function extractTextType1(url, text) {
    var matrix = [];
    var map = [];
    var vaccines = [];
    var regionsTemp = [];
    var regions = [];
    var regionLength = [1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1];

    var textArray = text.split('\n');
    for(var i = 0; i < 23; i++) {
        matrix[i] = textArray[i].split(' ');
    }

    matrix[0].shift();
    vaccines = matrix[0];
    map[0] = vaccines;

    for(var i = 0; i < regionLength.length; i++) {
        var j = i + 1; 
        var indexToRemove = 0;
        var numberToRemove = regionLength[i];
        var region = matrix[j].splice(indexToRemove, numberToRemove);
        regionsTemp.push(region);
        map[j+1] = matrix[j];
    }

    for(var i = 0; i < regionsTemp.length; i++) {
        var region = '';
        if(regionLength[i] > 1) {
            region = regionsTemp[i].join(' ');
        }
        else {
            region = regionsTemp[i].join('');
        }
        regions.push(region);
    }
    map[1] = regions;

    for(var i = 0; i < map.length; i++) {
        for(var j = 0; j < map[i].length; j++) {
            map[i][j] = map[i][j].replace(/\r/g, '');
        }
    }

    vaccines = map.shift();
    regions = map.shift();

    var thisJson = map.reduce(function(result, v, i) {
        v.forEach(async function(o, k) {
            var obj = createJsonObjectCoverage(url.year, 'Italy', vaccines[k], regions[i], o);
            // save on db
            const queryInsertDoNothing = {
                text: 'INSERT INTO coverages (vaccine, country, region, year, value) VALUES ($1, $2, $3, $4, $5) ON CONFLICT (vaccine, country, region, year, value) DO NOTHING;',
                values: [vaccines[k], 'Italy', regions[i], url.year, o]
            };
            var printText = '[INSERT Italy IN coverages]';
            var queryRes = await postgreSQLlib.query(queryInsertDoNothing, printText);
        });
        return result;
    }, jsons);
}

async function extractTextType2(url, text) {
    // similar code to extractTextType1(url, text)
}

function createJsonObjectCoverage(year, country, vaccine, region, coverage) {
    return {
        year: year, 
        country: country, 
        region: region, 
        vaccine: vaccine, 
        coverage: coverage
    };
}

module.exports = methods;

问题是数据库中的插入不能正常工作。

使用 scraperCov.js 运行 app.js 的结果是：

START

Connected to db at localhost:5432 as admin (pass: admin)
[CREATE TABLE coverages] OK query

COUNTRY: Albania

COUNTRY: Austria
[INSERT Albania IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query

COUNTRY: Belgium
[INSERT Austria IN coverages] OK query
[INSERT Austria IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query
[INSERT Belgium IN coverages] OK query

Connection has ended

FINISH
[INSERT Belgium IN coverages] ERR query

从打印件中可以看出，最后会出现错误，因为在插入结束之前连接已关闭。此外，插入不是有序的（在单词COUNTRY: Albania下，没有任何内容，而在单词COUNTRY: Austria下有一些与阿尔巴尼亚相关的查询的结果等。）。

使用 scraperCovIt.js 运行 app.js 的结果是：

START

Connected to db at localhost:5432 as admin (pass: admin)
[CREATE TABLE coverages] OK query

Connection has ended

FINISH

在这种情况下，插入不会完全执行。

我该如何解决？

这些是我试图解决这个问题的日子，但我不知道该怎么做。这是我第一次使用async/await而且我遇到了很多麻烦。

感谢任何想要帮助我的人

Answer 1

正如我们在评论中所讨论的那样，这里有很多错误。以下是部分概念列表：

await仅等待异步操作。在承诺以外的任何事情上使用await并没有做任何有用的事情。它没有神奇的力量来知道什么时候进行一些底层的异步操作。 await只遵循承诺。

await在.forEach()循环内不会暂停该循环的执行。

不要混合回调代码和承诺代码。将它们混合起来真的很难让它们正常工作。如果你有一些只接受回调的代码，那么将它转换为一个返回promise的新函数。您通常可以使用util.promisify()在一行代码中创建新函数。
我不可能攻击你的整个代码，因为我甚至都不知道它是做什么的，但我会挑选一些例子并告诉你如何修复它们。我开始查看返回promise的extractText()（仅因为它声明为async，但该承诺根本没有连接到其中的异步操作。
这让我了解了extractText()调用的一些功能，例如extractTextType1()，因此我将首先向您展示如何解决此问题。

在extractTextType1()中，您在await postgreSQLlib.query(...)循环内的.forEach()循环内使用.reduce()。 await不会导致这些类型的循环中的任何一个暂停。因此，extractTextType1()函数将在完成任何查询之前很久就返回。由于看起来这些查询（实际上是插入的）不必排序并且可以并行运行，我们可以简单地将所有查询中的promise收集到一个数组中，然后使用Promise.all()来跟踪它们何时都完成了。

该代码如下所示：

function extractTextType1(url, text) {
    var matrix = [];
    var map = [];
    var vaccines = [];
    var regionsTemp = [];
    var regions = [];
    var regionLength = [1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1];

    var textArray = text.split('\n');
    for(var i = 0; i < 23; i++) {
        matrix[i] = textArray[i].split(' ');
    }

    matrix[0].shift();
    vaccines = matrix[0];
    map[0] = vaccines;

    for(var i = 0; i < regionLength.length; i++) {
        var j = i + 1; 
        var indexToRemove = 0;
        var numberToRemove = regionLength[i];
        var region = matrix[j].splice(indexToRemove, numberToRemove);
        regionsTemp.push(region);
        map[j+1] = matrix[j];
    }

    for(var i = 0; i < regionsTemp.length; i++) {
        var region = '';
        if(regionLength[i] > 1) {
            region = regionsTemp[i].join(' ');
        }
        else {
            region = regionsTemp[i].join('');
        }
        regions.push(region);
    }
    map[1] = regions;

    for(var i = 0; i < map.length; i++) {
        for(var j = 0; j < map[i].length; j++) {
            map[i][j] = map[i][j].replace(/\r/g, '');
        }
    }

    vaccines = map.shift();
    regions = map.shift();

    let promises = [];
    var thisJson = map.reduce(function(result, v, i) {
        v.forEach(async function(o, k) {
            var obj = createJsonObjectCoverage(url.year, 'Italy', vaccines[k], regions[i], o);
            // save on db
            const queryInsertDoNothing = {
                text: 'INSERT INTO coverages (vaccine, country, region, year, value) VALUES ($1, $2, $3, $4, $5) ON CONFLICT (vaccine, country, region, year, value) DO NOTHING;',
                values: [vaccines[k], 'Italy', regions[i], url.year, o]
            };
            var printText = '[INSERT Italy IN coverages]';
            promises.push(postgreSQLlib.query(queryInsertDoNothing, printText));
        });
        return result;
    }, jsons);
    return Promise.all(promises);
}

现在extraTextType1()返回一个只有在内部完成所有异步操作后才能解析的promise。如果其中任何一个失败，它将拒绝。

另请注意，extraTextType1()不再声明为async，因为没有使用await。它只是直接返回一个承诺。如果你需要对这些插入进行排序，那么循环需要更彻底的重写才能一次完成。

假设您对extraTextType2()应用了类似的修补程序，现在让我们修复包含函数extractText()。在这里，我们宣传textract.fromUrl()，因此我们不会尝试混合回调和承诺，我们会将.forEach()循环更改为for/of循环，以便await可以使用循环。然后，从await

console.log()

const util = require('util');
const textractFromUrl = util.promisify(textract.fromUrl);

async function extractText() {
    var config = {
        preserveLineBreaks: true
    };
    for (let url of urls) {
        let text = await textractFromUrl(url.link, config);
        switch(url.year) {
            case '2011': 
            case '2012':
                await extractTextType1(url, text);
                break;
            case '2013': 
                await extractTextType2(url, text);
                break;
            default:
                console.log('Error: no case');
        }
    }
}

然后，您可以通过更改以下内容来清除下载功能：

methods.download = async function(req, res) {
    await extractText();
}

到此：

methods.download = function(req, res) {
    return extractText();
}

在完成数据库中的插入之前关闭连接

1 个答案: