Ufdjrw

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);
 );
);

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.