同步迭代异步函数

Question

I have a function which reads data from oracle database, excel file and does some operations on the data and then stores the result data in an excel file.

const app = require('./index.js');
app('ZR_CUSTOMER_INVOICES Functional Specification')

const azureFunction = require('./connections/azureConnection');
const idsFunction = require('./connections/idsconnection');
const xlsFunction = require('./connections/readExcel');
const writeToExcel = require('./connections/writeToExcel');
var azureData;
var idsData;
var xlData;
var xlColumns;
var azureColumns;
var idsColumns;
var resultData;
var table_name;
var file_name='';
function app(fileName){
  file_name=fileName
  xlsFunction(file_name,xlCallback);
}
function xlCallback(xlresult,tName){
  table_name=tName;
  xlData=xlresult
  xlColumns=xlData.map((a,i)=>{
    return a.Columns
  })
  var azquery=`exec sp_columns  ${table_name}`
  azureFunction(azquery,acallback);
}
function acallback(azresult){
  // let table_name=xlData[0]['View Name']
  let idsquery=`select COLUMN_Name from ids_columns where table_id = (select table_id from ids_tables where table_name ='${table_name}')`;
  azureData=azresult;
  azureColumns=azureData.map((a,i)=>{
    return a.value
  })
  idsFunction(idsquery,icallback);
}
function icallback(idsresult){
  idsData=idsresult;
  idsColumns=idsresult.rows.map((a,i)=>{
    return a[0]
  })
  finalFunction()
}
function finalFunction(){
  resultData=xlData.map((a,i)=>{
    if(a.Columns==''){
      return;
    }
    a['inIds?']=idsColumns.includes(a.Columns);
    a['inAzure?']=azureColumns.includes(a.Columns);
    return a;
  })
  resultData=resultData.filter((a,i)=>{
    return a!==undefined;
  })
  // console.log(resultData);
  writeToExcel(resultData,file_name)
  console.log('done');
}

module.exports=app;

this is working fine.

but if I make function call to app twice.

const app = require('./index.js');
app('ZR_CUSTOMER_INVOICES Functional Specification')
app('ZR_CONTACTS Functional Specification')

I am getting output as done only once and then the control also doesn't break.

I think there is some problem with connections to database, so I want to do this synchronously and check.

//comment me if you need any code.

Answer 1

You have a bunch of variables (eg var azureData; ) which are scoped to the module.

When you call the function twice, both sets of function calls will share those variables.

In particular, this means that file_name=fileName will set file_name to 'ZR_CUSTOMER_INVOICES Functional Specification' and then to 'ZR_CONTACTS Functional Specification' , and both calls will continue to use the variable with the value 'ZR_CONTACTS Functional Specification' .

Define those variables inside the scope of app . Then define all the functions which need to access them inside of app too so that the variables are in scope for them.

Each call to app will then have its own set of variables and they won't overwrite each other.

Answer 2

I have solved the problem using callbacks.

const azureFunction = require('./connections/azureConnection');
const idsFunction = require('./connections/idsconnection');
const xlsFunction = require('./connections/readExcel');
const writeToExcel = require('./connections/writeToExcel');
const done = require('./app');
var azureData;
var idsData;
var xlData;
var xlColumns;
var azureColumns;
var idsColumns;
var resultData;
var table_name;
var file_name='';
function app(fileName){
  file_name=fileName
  xlsFunction(file_name,xlCallback);
}
function xlCallback(xlresult,tName){
  table_name=tName;
  xlData=xlresult
  xlColumns=xlData.map((a,i)=>{
    return a.Columns
  })
  var azquery=`exec sp_columns  ${table_name}`
  azureFunction(azquery,acallback);
}
function acallback(azresult){
  // let table_name=xlData[0]['View Name']
  let idsquery=`select COLUMN_Name from ids_columns where table_id = (select table_id from ids_tables where table_name ='${table_name}')`;
  azureData=azresult;
  azureColumns=azureData.map((a,i)=>{
    return a.value
  })
  idsFunction(idsquery,icallback);
}
function icallback(idsresult){
  idsData=idsresult;
  idsColumns=idsresult.rows.map((a,i)=>{
    return a[0]
  })
  finalFunction()
}
function finalFunction(){
  resultData=xlData.map((a,i)=>{
    if(a.Columns==''){
      return;
    }
    a['inIds?']=idsColumns.includes(a.Columns);
    a['inAzure?']=azureColumns.includes(a.Columns);
    return a;
  })
  resultData=resultData.filter((a,i)=>{
    return a!==undefined;
  })
  // console.log(resultData);
  writeToExcel(resultData,file_name)
  console.log('done');
  done.onDone()
}

module.exports=app;

const app = require('./index.js');
app('ZR_CUSTOMER_INVOICES Functional Specification')
function onDone(){
    app('ZR_CONTACTS Functional Specification')
}
exports.onDone=onDone

and it worked.