CODEWITHSUNDEEP
node.jspromiseknex.js
VericalId
VericalId

Reputation: 105

How to properly loop through asyncronous knex calls?

I have a program that depending on the size of an array that is being sent from the front end then I have to loop through making knex call to a database then return those values to the front end.

I have tried what some other people have suggested using Promise.all() and the map() function such as:

const req=Json.parse(datafromFE)

const neededvar={
   result1="",
   result2=[]
}

var call1=knex.select('field1').from('Table1').then(result=>{neededvar.result1=result});

function getData(current,i,knex){
  knex.select('data').from('table').where('data','=',current.field)
 .then((result)=>{
   neededvar.result2[i]=result*neededvar.result1 
   return(neededvar.result2)
})
}

Promise.all([call1,req.map((current,i)=>{getData(current,i,knex)}])
.then((values)=>{
console.log(values)
e.returnValue=neededvar//using electron ipcRenderer I believe is similar to 
                      //vanilla nodejs backend res.json('placedatahere')
//so just think about 
//res.json(neededvar)
})

however,when I run the call the console.log(values) returns undefined for the array map calls but not for the first knex select call as here:

console.log(neededvar)
//[result1,undefined,undefined...]

I have tried to check if its my knex call, doing so by just calling the call1 function inside the map but still returns undefined.

var call1=knex.select('field1').from('Table1')

Promise.all(req.map((current,i)=>{call1}).then((result)=>{
console.log(result)
})
//output:[undefined,...,undefined]

I could just call the API from the front end several times but I just though this would be the most efficient way .If there is any guidance that can be given I would appreciate it much

-------Edit-------

Must remember to add all returns to all functions

function getData(current,i,knex){
  knex.select('data').from('table').where('data','=',current.field)
 .then((result)=>{
   neededvar.result2[i]=result*neededvar.result1 
   return(neededvar.result2)
})
}

should really be 

function getData(current,i,knex){
  return(knex.select('data').from('table').where('data','=',current.field)
 .then((result)=>{
   neededvar.result2[i]=result*neededvar.result1 
   return(neededvar.result2)
}))
}

the same goes to the other knex call

Upvotes: 0

Views: 1545

Answers (1)

Rich Churcher
Rich Churcher

Reputation: 7654

The main issue is that the function you pass to .map returns undefined:

Promise.all([call1,req.map((current,i)=>{getData(current,i,knex)}])

You probably meant:

Promise.all([
  call1,
  ...req.map((current,i) => getData(current,i,knex)
])

This will combine the first query with the array of queries generated out of req.

You should also return the promise from getData:

function getData(current,i,knex){
  knex.select('data').from('table').where('data','=',current.field)

should be:

function getData(current,i,knex){
  return knex.select('data').from('table').where('data','=',current.field)

Upvotes: 1

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