I've set up a function for my Express JS endpoint to 'await' to get a result from a Mongo DB using Mongo JS.
Function:-
async function getIntroducer(company){
const intro = await dbIntro.collection('introducers').findOne({company: company}, function(err, doc) {
console.log("๐ ~ file: app.js ~ line 289 ~ intro ~ doc.introducer", doc.introducer)
return doc.introducer
});
return intro
//return intro;
};
Express JS Endpoint:-
app.post(
"/case",
passport.authenticate("accessToken", { session: false }),
async function (req, res) {
const body = req?.body;
const intro = await getIntroducer(req.user.company);
console.log("๐ ~ file: app.js ~ line 1152 ~ intro", intro)
Current behaviour, :-
๐ ~ file: app.js ~ line 1152 ~ intro undefined
Then the result sends, then thereafter I get this in console (aka it's not awaiting):-
๐ ~ file: app.js ~ line 289 ~ intro ~ doc.introducer 347501
I've also tried completely getting rid of 'const intro' and just straight returning it. And I've also tried getting rid of the callback function but MongoJS says 'CB is not a function'
Any help please?
You're mincing different styles of asynchronous implementations (callback and promise) when querying the collection.
Seeing as the mongojs library supports only the callback style. You need to promisify the findOne operation to await it.
There is the promisify library in the util module that can aid in this goal inasmuch as the callback signature is a function that is called with an error and/or a result.
For example, to promisify the findOne so that it can be awaited, you can write
const util = require('util');
async function getIntroducer(company){
const findOneDbIntro = util.promisify(dbIntro.collection('introducers').findOne);
let intro;
try {
intro = await findOneDbIntro({company: company});
}
catch (err)
{
// log error with your logging library.
}
//...
}
This gives a similar result to doing by hand. The Promise object is well documented on MDN:
async function getIntroducer(company){
let intro;
try {
intro = await new Promise(
(resolve, reject) => {
dbIntro.collection('introducers').findOne({company: company},
function (err, doc) {
if(err) {
reject(err);
}
resolve(doc);
});
});
} catch (err)
{
// log error with your logging library.
}
//...
}