Firebase collection becomes an array with null in Firebase JSON API

Question

I have a Firebase collection that looks like this:

Source: https://weld-development-tom.firebaseio.com/projects/5649ddc3f709a10c003cf031/screens (need auth)

But when I request it over the Firebase JSON API, it looks like this:

[
  null,
  {
    "dateUpdated" : 1454489265605,
    "elements" : { /* removed to make question shorter */ },
    "name" : "Screen 1",
    "slug" : "screen-1"
  }
]

Source: https://weld-development-tom.firebaseio.com/projects/5649ddc3f709a10c003cf031/screens.json?print=pretty

How can I get the real screens collection through the JSON API?

Frank van Puffelen · Accepted Answer · 2016-02-03 15:34:28Z

2

This is how the Firebase database handles arrays.

In your situation, if you want an object rather than an array you'll need to change your keys from indexed based like an array. Unless the 1,2,3 ordering is important I would recommend using the .push() id generated from the Firebase SDK, or by doing a POST in over the REST API.

Check out the documentation on Arrays in Firebase data, which contains the code snippet below.

// we send this
['a', 'b', 'c', 'd', 'e']
// Firebase stores this
{0: 'a', 1: 'b', 2: 'c', 3: 'd', 4: 'e'}

// since the keys are numeric and sequential,
// if we query the data, we get this
['a', 'b', 'c', 'd', 'e']

// however, if we then delete a, b, and d,
// they are no longer mostly sequential, so
// we do not get back an array
{2: 'c', 4: 'e'}

edited Feb 3, 2016 at 15:34

Frank van Puffelen

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answered Feb 3, 2016 at 12:35

David East

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4 Comments

Tom Söderlund Over a year ago

I understand that it becomes an array, but where does the null object come from? It's not present in my collection.

Dan Getz Over a year ago

Probably because Arrays are 0-based, and null fills in for the 0 element.

David East Over a year ago

^- this. Your index first index is 1, so since Array's must start with 0, Firebase backfills the first element in the array with null.

JaakL Over a year ago

Well this is not that simple. Just experienced that if you delete one element from the middle, e.g. 'c', then you probably end up with array with 'null', like ['a', 'b', null, 'd', 'e'] . When the array is nullified and when objectified should be better defined by firebase, too much magic is never good.

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