Combine results from two sets of data into an array by utilizing the _.each() method

What I'm aiming for:

I aim to make a call to an API and within that API, I want to achieve the following:

  1. Locate Bills
  2. Retrieve all transactions associated with each bill (using billId)
  3. Present the values in a JSON ARRAY

Here is an example representation of the bill array: 

{ _id: 549bf0597886c3763e000001,
billName: 'Leasing',
startDate: Thu Dec 25 2014 01:00:00 GMT+0100 (CET),
endDate: Sun Oct 15 2017 00:00:00 GMT+0200 (CEST),
amount: 16500,
type: 4,
timestamp: Thu Dec 25 2014 12:09:13 GMT+0100 (CET),
__v: 0 },
{ _id: 54a014bfac01ca3526000001,
billName: 'Test',
startDate: Tue Oct 28 2014 01:00:00 GMT+0100 (CET),
endDate: Wed Dec 20 2017 00:00:00 GMT+0100 (CET),
amount: 1000,
type: 4,
timestamp: Sun Dec 28 2014 15:33:35 GMT+0100 (CET),
__v: 0 }

Using the array obtained in the first step, I intend to query the transactions collection and retrieve each transaction for every bill. The transformation would look like this:

{ _id: 549bf0597886c3763e000001,
billName: 'Leasing',
startDate: Thu Dec 25 2014 01:00:00 GMT+0100 (CET),
endDate: Sun Oct 15 2017 00:00:00 GMT+0200 (CEST),
amount: 16500,
type: 4,
timestamp: Thu Dec 25 2014 12:09:13 GMT+0100 (CET),
__v: 0 ,
transactions: {
  { 
    "_id" : ObjectId("549ea8c957b654ef64000003"), 
    "billId" : "5499aece1d7be6c6a3000001", 
    "paymentDate" : ISODate("2014-12-27T12:40:41.311+0000"), 
    "amount" : NumberInt(2400), 
    "timestamp" : ISODate("2014-12-27T12:40:41.311+0000"), 
    "__v" : NumberInt(0)
  }
  { 
    "_id" : ObjectId("549ea9446163b3c666000001"), 
    "billId" : "5499aece1d7be6c6a3000001", 
    "paymentDate" : ISODate("2014-12-27T12:42:44.975+0000"), 
    "amount" : NumberInt(2400), 
    "timestamp" : ISODate("2014-12-27T12:42:44.975+0000"), 
    "__v" : NumberInt(0)
  }

}
},
{ _id: 54a014bfac01ca3526000001,
billName: 'Test',
startDate: Tue Oct 28 2014 01:00:00 GMT+0100 (CET),
endDate: Wed Dec 20 2017 00:00:00 GMT+0100 (CET),
amount: 1000,
type: 4,
timestamp: Sun Dec 28 2014 15:33:35 GMT+0100 (CET),
__v: 0 }

While I have been successful in obtaining the bill IDs from the bill collection, I am facing difficulties in extracting the transaction IDs into an array.

My current approach is as follows:

app.get('/getbills', function(req,res) {

    function getTransactions(item, key){

            var billId = item._id;

             Transactions.find({billId : billId}, function(err, transactions){ // TODO: Needs to look for transactions inside the date.
                if (err)
                    console.log('error: '+ err)
                else if (transactions.length !== 0){
                    return transactions;
                }
            });                

        };

    Bills.find({type: bill_type}).find(function(err, bills){
        if(err)
            res.send(err);

        details.bills = bills;

        details.bills.transations = _.each(bills, getTransactions);

     res.send(details);  
    });

});

I am utilizing _.each to extract the billId and query the transactions table, but I have not found sufficient examples to guide me on the implementation of this function in the manner I am attempting. It's possible that my approach is incorrect.

Any assistance or insights would be greatly appreciated.

Thank you in advance.

javascriptarraysmongodbmongooseunderscore.js

Answer №1

It seems like you may not be waiting for the second call to finish, resulting in incomplete data. The return statement might not be working as intended.

To dive deeper into this issue, consider learning more about handling asynchronicity in JavaScript.

While the current code may work, it's important to understand how it functions. The trySend function serves as a basic synchronizer, ensuring all data is available before responding. It may not be the most efficient solution, but it's a straightforward one.

app.get('/bills', function( req, res ) {
  Bills.find({type: bill_type}, function( err, bills ) {
    if( err ) return res.send(err);

    var tries = 0;
    var details = { bills: bills };
    var trySend = function (){
      tries++;
      if (tries === bills.length) {
        res.send(details);  
      }
    };

    bills.forEach( function ( bill ) {
      Transactions.find({billId : bill._id}, function ( err, transactions ) {
        if ( err ) return res.send( err );

        bill.transations = transactions;
        trySend();
      });  
    });        
  });
});

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