While working with an Express JS application connected to a mySQL database, I encountered an issue when trying to fetch data from a pre-defined route/query:
// customers.model.js
CUSTOMERS.getAll = (result) => {
let query = "SELECT * FROM customers"
sql.query(query, (err, res) => {
if (err) {
console.log("error: ", err)
result(null, err)
return
}
result(null, res)
})
}
// customers.controller.js
// The GET customers route is set up to display all the available customer data.
const CUSTOMERS = require("../models/customers.model.js")
exports.findAll = (req, res) => {
return CUSTOMERS.getAll((err, data) => {
if (err)
res.status(500).send({
message: err.message ||
"Some error occurred while retrieving customers...",
})
else res.send(data)
})
}
In payments.controller.js, my aim is to retrieve all users initially in order to manipulate the data:
// payments.controller.js
// The GET payments route is designed to fetch customer data, perform operations on it, and output calculated results based on this data
const CUSTOMERS = require("../models/customers.model.js")
exports.calculateAll = (req, res) => {
const customers = CUSTOMERS.getAll((err, data) => {
console.log('this always has correct data', data)
if (err) return err
else return data
})
console.log('this is always undefined', customers)
...
res.send(whatEverCalculatedData)...
}
However, I constantly encounter the issue of data being undefined. What could possibly be wrong with my implementation above, and how should I correctly invoke one route inside another?
I've noticed similarities with this question, but I'm struggling to apply solutions to my specific scenario.