How to respond with array of query results in Node/ Express/ Postgresql? - node.js

Question

newbie here. I am trying to fetch an array of objects from my local database through two select queries, using knex.js and postgresql like so:
app.get('/trips/:name', (req, res) => {
const {name} = req.params;
db.select('tripid').from('member')
.where('name', '=', name)
.then(data => {
const array = data.map(elem => {
db.select('tripname')
.from('trip')
.where('id', '=', elem.tripid)
.then(obj => {
array.push(obj[0])
})
})
return array
})
.then(arr => res.json(arr))
.catch(err => res.status(400).json(err))
})
I want to push all the objects that the second query returns into an array and respond to the front end. However, it always returns an empty array, which I suspect because
.map
is asynchronous, so the array is returned before the loop finishes. How can I fix this? Any help is appreciated. Thanks. Sorry if my code is hard to read.

Answer 1

try this way using async await :
app.get('/trips/:name', async (req, res) => {
try{
const {name} = req.params;
let arr = await db.select('tripid').from('member').where('name', '=', name);
if(arr && arr.length>0){
for(let item of arr){
let tripResult = await db.select('tripname').from('trip').where('id', '=', item.tripid).catch(e=>e);
item.trip = tripResult && tripResult[0]? tripResult[0]:null;
}
}
return res.json(arr);
}catch(error){
return res.status(400).json(error);
}
}
2nd way :
app.get('/trips/:name',(req, res) => {
const {name} = req.params;
db.select('tripid').from('member').where('name', '=', name)
.then(arr =>{
Promise.all(arr.map(item =>{
db.select('tripname')
.from('trip')
.where('id', '=', item.tripid)
.then((tripResult=>{
item.trip = tripResult && tripResult[0]? tripResult[0]:null;
return item;
}).catch(e=>e);
})
).then(arr => {
return res.status(200).json(arr);
})
}).catch(err => res.status(400).json(err));