How can an array object be reconstructed by iterating through MongoDB documents in JavaScript?

Currently in the process of reconstructing an arrayObject by iterating through elements obtained from an ajax .get request of MongoDB documents.

The arrayObject is close to being correct, but it lacks proper comma separation between the documents within the array.

This appears to be causing the issue where

console.log(arrayObject[0].name);
returns undefined.

When attempting to use an if/else statement to avoid having a leading comma, the if condition is skipped.

function reBuild(returnValue)
{
  var docs = returnValue;
  var returnedVal = [];
  for (var i=0; i<docs.length; i++){

    if (returnedVal.length === 0)
    {
      returnedVal.push('{' + 'title: "' + docs[i].title + '", quantity: ' + docs[i].quantity + ', _id: "' + docs[i]._id + '"}');
    }
    else
    {
      returnedVal.push(', {' + 'title: "' + docs[i].title + '", quantity: ' + docs[i].quantity + ', _id: "' + docs[i]._id + '"}');
    }

    console.log(returnedVal[i]);

  }
  console.log(returnedVal[0].title);
}

console.log(returnedVal[i]);

[15:20:02.946] "{title: "Sample1", value: 2, _id: "530c12c66e6b0de318000001"}"
[15:20:02.946] ", {title: "Sample2", value: 4, _id: "530c12cc6e6b0de318000002"}"

Retrieving MongoDB data via .get:

function getAll(res) {

    db.collection('demo').find().sort( { value: 1 } ).toArray(function (err, docs) {
        console.log("Received Documents: " + utils.inspect(docs));

        // Each document has the structure: { _id: ObjectID, title: 'string', quantity: int}

        res.json({docs: docs});

    });
}

The output of the documents in the terminal console looks like this:

[ { _id: 530c12c66e6b0de318000001,
    title: 'Sample1',
    quantity: 2 },
  { title: 'Sample2',
    quantity: 4,
    _id: 530c12cc6e6b0de318000002 } ]

I am aiming to retrieve an arrayObject containing MongoDB documents, create a new variable from the arrayObject using object.foo, and then reconstruct an arrayObject with all the foobar values once they are ranked.

There is another function responsible for performing calculations on variables for ranking purposes.

Answer №1

After the recent update

Consider the information provided in the variable returnValue, which is shown as (like your example)

[ 
  { _id: 530c12c66e6b0de318000001, title:'Sample1', quantity: 2 },
  { _id: 530c12cc6e6b0de318000002, title:'Sample2', quantity: 4} 
]

that is being passed to the reBuild() function like this: reBuild(returnValue)

The 'reBuild()' function is designed to convert the 'returnValue' format into a different array:

Your example ..

 returnedVal.push(', {' + 'title: "' ...

...has some issues, such as sending a leading comma to the push method and problems with quote manipulation for creating strings or custom JSON format.

Let's simplify that function like this

function reBuild(arr) {

 var returnedVal = [];
 for (var i=0, len=returnValue.length; i < len; ++i){
   var newval = {_id:arr[i]._id,title:arr[i].title,quantity:arr.arr[i].quantity};
   returnedVal.push(newvalue);
 }

 console.log(returnedVal);
 return (returnedVal);

}

This works, but what did we achieve? Essentially, we just reconstructed the 'returnedVal' array exactly as it was before.

Now, let's analyze the ajax data request you provided

db.collection('demo').find().sort( { value: 1 } ).toArray(function (err, docs) {
    console.log("Got the Docs: " + utils.inspect(docs));
    res.json({docs: docs});

});

We seem to have missed the connection to the rebuild() function here.

Considering the res.json({docs: docs}); part (a function to respond with data as JSON), should the flow be something like this?..

db.collection('demo').find().sort( { value: 1 } ).toArray(function (err, docs) {

    /* pass and rebuild the data array before 'jsonifying' it */
    var rebuiltDocs = reBuild(docs); 
    res.json({docs: rebuiltDocs});

});

I made assumptions about how your app functions. The essential point to grasp is that once you JSON.stringify() an object, it becomes a string representation of your JavaScript object.

If you need to use JSON for transmitting data over HTTP (its primary purpose), manipulate your data prior to converting it to JSON format.

To revert back from JSON, utilize JSON.parse(docs)

  • For processing Data within your application (if arriving as JSON), employ JSON.parse()
  • For transferring data between systems, resort to JSON.stringify()

If my explanation seems lacking, I hope it sheds some light on why manual tweaking of arrays may have been necessary in certain instances.

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