Unhandled Rejection: TypeError: Cannot read property 'Symbol(Symbol.iterator)' of undefined

[mandaputtra]

How to use highlandjs with async await ? Here my code, simple one First i read the csv file, using fast-csv to remove first line and make the and for each line i check it there is a data or not if there is a data its console.log() some message. if not the data saved but. for now if there is a data the data still saved and not console.log() my message. and if every stream is pass it returning same error message

Unhandled Rejection: TypeError: Cannot read property 'Symbol(Symbol.iterator)' of undefined

LIbrary im using :

• Fast-Csv
• Bookshelf
• fs

here the full code :

DescController.CompaniesCsv = async (req, res, next) => {

  const file = fs.createReadStream(path.join(req.files[0].path), 'utf8').pipe(csv({headers : true}))

  // Read data streams from here with highlandjs
  _(file)
      .each(async (companyData) => {
        // console.log(companyData)
        const sectorName = capitalize(companyData.sector);
        const companyName = capitalize(companyData.name);
        const companyCountry = capitalize(companyData.country);

        const getSector = await Sector.get({ name: sectorName });
        const getCompany = await Company.get({ name: companyName });
        const getCountry = await Country.get({ name: companyCountry });

        const [sector, company, country] = await Promise.all([getSector, getCompany, getCountry]);

        let serSector;
        if(!sector) {
          console.log('Please add a sector first on the admin');
        } else {
          serSector = sector.serialize()
        }

        let serCountry;
        if(!country) {
          serCountry = await Country.forge({ name: companyData.name, order: 1 }).save();
        } else {
          serCountry = country.serialize()
        }

        if(company) {
          console.log('There is a company', company.serialize());
        } else {
          const saveCompany = await Company.forge({ name: companyData.name, country_id: serCountry.id , user_id: req.user.id }).save();
          const insertSector = await CompanySector.forge({ company_id: saveCompany.get('id'), sector_id: serSector.id }).save();
          await Promise.all(...insertSector)
        }
      })

  return res.redirect('companies');
}

the full error message :

::ffff:127.0.0.1 - - [08/Dec/2018:08:19:52 +0000] "GET /companies HTTP/1.1" 200 - "http://localhost:4000/companies" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0"
Unhandled Rejection: TypeError: Cannot read property 'Symbol(Symbol.iterator)' of undefined
    at Function.all (<anonymous>)
    at _callee2$ (C:\DATA\source\code\build\modules\desc\controller.js:200:44)
    at tryCatch (C:\DATA\source\code\node_modules\regenerator-runtime\runtime.js:65:40)
    at Generator.invoke [as _invoke] (C:\DATA\source\code\node_modules\regenerator-runtime\runtime.js:303:22)
    at Generator.prototype.(anonymous function) [as next] (C:\DATA\source\code\node_modules\regenerator-runtime\runtime.js:117:21)
    at step (C:\DATA\source\code\build\modules\desc\controller.js:46:191)
    at C:\DATA\source\code\build\modules\desc\controller.js:46:361
    at <anonymous>

[mandaputtra]

Solved the problem was on the await Promise.all(...insertSector) I'm still open for feedback on using async await with highlandjs. thanks

[vqvu]

async await works with Promises, so you need to convert highland streams to and from promises to use it. To convert from promises, use the contructor (_(aPromise)). To convert to promises, use toPromise.

In your example, you can do something like this

DescController.CompaniesCsv = async (req, res, next) => {

  const file = fs.createReadStream(path.join(req.files[0].path), 'utf8').pipe(csv({headers : true}))

  // Read data streams from here with highlandjs
  await _(file)
      // Create promises that represent the async computations.
      .map(async (companyData) => {
        ...
      })
      // Convert the promises to streams and wait for them to complete.
      // You can replace flatMap(_) with map(_).merge() or map(_).mergeWithLimit(n) to increase
      // the amount of parallelism.
      .flatMap(_)
      // Throw away all of the results of the promises.
      .filter((ignored) => false)
      // Convert back to a promise so that you can await it.
      // Replace this with resume() if you want to return the redirect before you're done
      // with the async work.
      .toPromise(Promise)

  return res.redirect('companies');
}

[mandaputtra]

@vqvu is this still okay to .each and not .map ?

[vqvu]

Using each like you did originally is OK if you don't want to wait for the async computations to complete before you do the redirect.