How to transfer data of one collection into another of mongodb - mongodb

Question

Am working on nestjs.I have two collections one in orders and second is payment and i want to retrieve one single entry from orders collections and save that same entry into payment collection.
Here is the code of services:
async order(name){
const list=this.usersmodel.find({name:name}).exec()
//return list
try{
if(list){
const x=this.usersmodel.aggregate([
{$out:"payment"}
])
return "data saved in payment collection"
}
}
catch(error){
return(error.message)
}
}
Here is the code of controller:
#Get('orderdata')
async orderdata(#Body('name')name){
return this.usersService.order(name)
}
By using these code lines neither i got desired output nor i got any error. I got "data saved in payment collection" when am hitting API in postman but i didn't get the entries in my payment collection.

Answer 1

I think the issue is here, in this line
const list = this.usersmodel.find({ name: name }).exec()
this is an asynchronous block of code, so the next lines will be executed without waiting for this list to be resolved
you have to use await keyword to enforce javascript to wait until this line is executed before executing the next lines
const list = await this.usersmodel.find({ name: name }).exec()
also, the aggregate pipeline is taking the whole order documents to the payment collection, as there is no filtering applied to that orders in the aggregate pipeline
so you have to add $match stage to your aggregate pipeline, in order to add the list of orders that have the name you specified
also note that we need await in the aggregate too as this is an asynchronous block of code, so wait until this aggregation to be done then execute the return statement
so the whole function should look something like
async order(name) {
const list = await this.usersmodel.find({ name: name }).exec()
//return list
try {
if(list){
await this.usersmodel.aggregate([ // note the await here
{ $match: { name: name } }, // filtering the orders
{ $out: "payment" } // move them to the payment collection
])
return "data saved in payment collection"
}
}
catch (error) {
return(error.message)
}
}
hope it helps