mongoDB with nodejs return data

Question

I have my own class and method call findByIdDate() When I find the data then inside of db.collection() I will get result but if I want to return that data from my own method it will come back undefined. Could someone provide me example how to get the data please? I have been searching but I can not find any answers to this problem. I'm new to node and express My Method

findByIdDate(){
 let data = this.db.collection('journal').find({date: this.Date}).toArray((err, result) => {
 if(err){return console.log(err)}
 console.log(result) // I have data
 return result
 })
 return data
}

in my other file I use it like this

app.post('/id', (req, res) => {
 const DIARY = new diary('new', '16 January 2020', db)
 let result = DIARY.findByIdDate()
 console.log(result) // undefined 
});

• Ulrich Eckhardt: Can you extract and provide a minimal reproducible example please? Also, just wondering, could it be that the closure you give to toArray is executed asynchrously and that nothing is returned from toArray()? I'm not familiar with the JS MongoDB API, but async calls are not unheard of in the JS world.
• dikuw: You're probably console.logging result before it has been returned by findByIdDate(). There's a couple ways to handle this, the most modern being the use of async/await. This should lead you in the right direction.

Answer 1

It would be best to do away with callback functions and make the function async/await as:

async findByIdDate(){
 try {
 let data = await this.db.collection('journal')
 .find({date: this.Date})
 .toArray() // returns a promise which can be 'awaited'
 console.log(data)
 return data
 } catch (err) {
 console.error(err)
 throw err
 }
}

And use it in your route as

app.post('/id', async (req, res) => {
 try {
 const DIARY = new diary('new', '16 January 2020', db)
 let result = await DIARY.findByIdDate()
 console.log(result) 
 } catch(err) {
 console.error(err)
 } 
})

• wlh: is absolutely correct. Let me add: The reasoning is that the call to MongoDB is asynchronous. And the return statement in your original code outside of the find call was being called synchronously. It returned data as undefined because at the time it was called, data was still undefined. The previous statement had yet to return anything.