How do I add an empty array to an object array?

Question

basically I have an array that I pull data from. I would like to add a new array to it so I can pull additional data.

var myArray.libraries = []

gets items added via a for loop like this:

for(var x=0; x < items.length; x++){
    myArray.libraries ({ name: items(x).name, state: items(x).state});
}

that works great and I can get what I need from myArray.libraries .name. I need to add something like "books" so each entry can have it's list of books. There could be 1 or more books.

to be clear I'm using angular so I use something like this to output for each library:

<div ng-repeat="library in libraries">
    <p>{{library.name}}</p>
</div>

I just need to add books so I can loop through each book in that library:

<div ng-repeat="book in libraries.books">
    <p>{{book.name}}</p>
</div>

I tried using myArray.libraries.books = [] but that didn't add the collect to each library. I also tried myArray.libraries.push({ books: { } }) but that didn't have any affect and gave me an error that I couldn't push to myArray.libraries.books since books didn't exist.

EDIT

Here's some sample code. I'm using angular but the principle should be the same:

$scope.libraries= [];

//start loop to get the installations
for (var x = 0; x < res.rows.length; x++) {
    $scope.libraries.push({ ... , books: []});

    //run a new query to get the additional libraries info
    var booksQuery = query to get books;
    //run query to get results and loop through them
        for (var i = 0;i < res2.rows.length; i++) {
            $scope.libraries[x].books.push({ name: res2.rows.item(i).prodName });
        }
    });
}

EDIT

I ran some tests and it turns out when I do my second database call it doesn't know the original $scope exists.

I'm not sure I get it, you have an array, yet you're treating it like an object adding named keys to it, so it's no longer an array. The loop doesn't seem to do anything, it just overwrites the same property on each iteration, and now you want to add another named key to the array that isn't really an array anymore ? — adeneo
– adeneo, Commented Jun 5, 2015 at 18:14

taxicala · Accepted Answer · 2015-06-05 18:14:21Z

2

Try as follows:

for(var x=0; x < items.length; x++){
    myArray.libraries ({ name: items(x).name, state: items(x).state, books: []});
}

That should do the trick.

answered Jun 5, 2015 at 18:14

taxicala

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9 Comments

adeneo Over a year ago

I'm just really confused, is myArray.libraries an array, an object or a function ?

taxicala Over a year ago

As per the code you've posted, it seems like it's an array, containing objects inside. I've just added another key to the object you are pushing named books, that's an empty array as your question stated you wanted to do.

adeneo Over a year ago

Now I'm more confused, I'm not the OP ?

taxicala Over a year ago

my bad :) Did not realize you wheren't the OP

dcp3450 Over a year ago

@taxicala - it was my question not @adeneo's. Also, what you suggested placed books in the array but I can't push to it. When I do myArray.libraries.books.push({...}) I'm being told Unable to get property 'push' of undefined or null reference

|

kamil-mrzyglod · Accepted Answer · 2015-06-05 18:16:53Z

1

Basically the problem is that you are trying to push array to an array. You can push another array to your libraries, but to access books you have to use index to access specific item like myArray.libraries[0].books[0]

So I assume you have to change myArray.libraries.push({ books: { } }) to myArray.libraries.push({ books: [] })

answered Jun 5, 2015 at 18:16

kamil-mrzyglod

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Comments

Nikhil Aggarwal · Accepted Answer · 2015-06-05 18:14:35Z

0

I have created a plunker for you. Please refer to

"http://plnkr.co/edit/0FKg2fbe4CY11Oz6aSBF?p=preview"

$scope.libraries = {
    books : [
  {"name" : "book1"},
  {"name" : "book2"},
  {"name" : "book3"}
      ]


  };

answered Jun 5, 2015 at 18:14

Nikhil Aggarwal

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8 Comments

dcp3450 Over a year ago

Thanks for the plunker, and that's the result I want. I'm trying to figure out how to create an empty books inside my array so I can push new items to it via a loop.

dcp3450 Over a year ago

When I try that it just adds books to myArray not myArray.libraries and it place each book it's on array instead of grouping them...

Nikhil Aggarwal Over a year ago

I am not able to collect, Can you please send the updated code?

Nikhil Aggarwal Over a year ago

I have updated the plunker for your review. Please chek "plnkr.co/edit/0FKg2fbe4CY11Oz6aSBF?p=preview"

dcp3450 Over a year ago

I'm attempting something similar to what you're suggesting. Before I add books if I run this in the second loop $scope.libraries[x].books I get an empty array, as expected. but when I run $scope.libraries[x].books.push({...}) i get the error Unable to get property 'books' of undefined or null reference

|

Karuna Lakshman · Accepted Answer · 2015-06-06 20:30:26Z

0

This will help you.

DB calls are async, so the 2nd db call shouldn't be in loop. Please check if this works

$scope.libraries = [];  

  init();

  function init() {
    // do the first db transaction
  }

  // transaction1 callback
  function trans1Callback(result) {    
    addBooks(result);
  }

  var i = 0;

  function addBooks(result) {
      // to stop iteration at the end of records
      if (i >= result.rows.length) {
        return;
      }
      var item = result.rows.item(i);
      var data = {name: item.name, state: item.state, books: []};
      // do the second db transaction

      // transaction2 callback
      function trans2Callback(result2) {

          for (var j =0; j < result2.rows.length; j++) {
              var book = result.rows.item(j);
              data.books.push({ name: book.prodName });
          }
          // push to scope libraries
          $scope.libraries.push(data);
          // do increment
          i++;
          // Call addBooks again to process next record
          addBooks(result);
      }

  }

edited Jun 6, 2015 at 20:30

answered Jun 5, 2015 at 18:28

Karuna Lakshman

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2 Comments

dcp3450 Over a year ago

added some code so you can see more info, this includes some angular stuff too. Didn't want to overload the sample with my db calls though

Karuna Lakshman Over a year ago

I have edited my answer. Please let me know, if it solves your prob

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