Node express multiple queries in one route that depend on each other - node.js

Question

I am just about getting familiar with node and express and programming in general, but this is a more complex issue I am trying to solve. Please if you can provide with some best practice in this kind of scenario.
I am trying to run two queries to my database where the first one is dependent on the result of the first. Q1. Return a list of ids. Q2. Return id and coord for each of the ids. I want to respond with a json object that look something like this
[
{ id: 451, coords: 'POINT(12.5574 43.8351)' },
{ id: 56, coords: 'POINT(13.5574 44.8351)' }
]
Currently I cannot get it to work, I know there is probably several issues with my example code, but I have pretty much got stuck. Maybe I am overthinking this and make it harder than it is, or bad practice in general.
How can I run multiple queries where the second use the output from the first one and then build the correct object to respond with. Any pointers would be much appreciated.
router.get('/asset/:id', (req, res) => {
let latLngOfAssets = []
// get associated assets
function getConnectionsById() {
queries.getConnectionsById(req.params.id) // return list of objects
.then(data => {
if (data) {
data.forEach(function(element) {
getLatLngofAsset(element.til_poi_id) // for each id in list call function to get coordinate
});
} else {
throw new Error('No data returned');
}
console.log(latLngOfAssets) // What I want to respond with res.json(latlngofassets)
})
}
function getLatLngofAsset(id) {
queries.getPoilatlng(id) // Return geometry as text for asset with id
.then(data =>{
let newassetobj = {}
if (data) {
newassetobj["id"] = data.rows[0].id
newassetobj["coords"] = data.rows[0].st_astext
//console.log(newassetobj) // structure of each object { id: 451, coords: 'POINT(12.5574 43.8351)' }
latLngOfAssets.push(newassetobj) // making list of objects i want to respond with
} else {
throw new Error('Did not get any poi');
}
})
}
getConnectionsById()
.catch(err => { // {message: "Cannot read property 'then' of undefined", error: {…}}
console.error('Something went wrong', err);
});
});

Answer 1

You've done a good job separating out the two distinct sections of your code into separate functions - what you're missing is the ability to tie them together. This portion of your code is not doing what I think you are trying to accomplish:
data.forEach(function(element) {
getLatLngofAsset(element.til_poi_id)
});
Because getLatLngofAsset() is Promise-based* you need to use it like a Promise. You first need to make getLatLngofAsset return the Promise chain it creates. Then, it can be await-ed inside getConnectionsById using an async function:
function getConnectionsById() {
queries.getConnectionsById(req.params.id)
.then(data => {
if (data) {
data.forEach(async function(element) { // <-- note the async keyword here
await getLatLngofAsset(element.til_poi_id)
});
} else {
throw new Error('No data returned');
}
console.log(latLngOfAssets) // What I want to respond with res.json(latlngofassets)
})
}
This is a start - there are a couple more things we can tackle once you understand the relationship between the functions you have declared and the Promises they create & return.