我阅读了txt的每一行，并对其中的每一行执行了一些简单的数据库查询。

fillDatabase1做我想要的事情。它对每一行执行查询，当一切完成后，它等待数据库关闭，然后调用resolve。

fillDatabase2尽管与fillDatabase1非常相似，但似乎在执行每一行的查询之前运行了database.close，从而导致错误。

UnhandledPromiseRejectionWarning: Error: Cannot enqueue Query after invoking quit.

database.js

const mysql = require( 'mysql' )
const db_credentials = require('./config')

module.exports =  class Database {
    constructor() {
        this.connection = mysql.createConnection( db_credentials );
    }
    query( sql,args ) {
        return new Promise( ( resolve,reject ) => {
            this.connection.query( sql,args,( err,rows ) => {
                if ( err )
                    return reject( err );
                resolve( rows );
            } );
        } );
    }
    close() {
        return new Promise( ( resolve,reject ) => {
            this.connection.end( err => {
                if ( err )
                    return reject( err );
                resolve();
            } );
        } );
    }
}

readFile.js

const fs = require('fs')
const readline = require('readline')
const stream = require('stream')
const mydatabase = require('../database/database.js')

updateDatabase()

const updateDatabase = async () => {
    // 1) Fill Topics
    await fillDatabase1()
    console.log("fillDatabase1 completed")
    // 2) Fill database2
    await fillDatabase2()
    console.log("fillDatabase2 completed")
}

const fillDatabase1= () => {
    database = new mydatabase()
    return new Promise((resolve,reject) => {
        var instream = fs.createReadStream("C:\Users\prof_chaos\Desktop\mydata.txt")
        var outstream = new stream()
        var rl = readline.createInterface(instream,outstream)
        var lineCount = 0
        let outcome;

        rl.on('line',async function(line) {
            lineCount++;
            let data = line.split('|')
            let args = {mid: data[0],name: data[1],description: data[2],type: data[3]}
            let sql = 'INSERT INTO topics SET ?'
            outcome = await database.query(sql,args)
        })
        .on('close',() => {
            console.log(`Succesfully added ${lineCount} lines to topics table`)
            database.close().then(() => {
                console.log('db connection closed - filled topics')
                resolve()
            })
        })
    })
}

const fillDatabase2 = () => {
    return new Promise((resolve,reject) => {
        database = new mydatabase()
        var instream = fs.createReadStream("C:\Users\prof_chaos\Desktop\mydata2.txt")
        var outstream = new stream()
        var rl = readline.createInterface(instream,outstream)
        var lineCount = 0
        let topic;
        let sql;

        rl.on('line',async function(line) {
            lineCount++;
            let data = line.split('|')
            sql = 'SELECT id FROM topics WHERE mid = ? LIMIT 1'
            topic = await database.query(sql,[data[0]])
            if(topic[0]) { // If SELECT found something
                let args = {predicate: data[1],value: data[2],topic_id: topic[0].id}
                sql = 'INSERT INTO topics_predicates_values SET ?'
                let outcome = await database.query(sql,args)
            } else {
                console.log("mid " + data[0] + " not found in database")
            }
        })
        .on('close',() => {
            database.close().then(() => {
                console.log(`Succesfully added ${lineCount} lines to topics_predicates_value table`)
                resolve()
            })
        })
    })
}