I have a node in this form:

index
   $categoryId
     $productId

I wish to retrieve primarily a list of the keys of index, thus an object filled with all the available $categoryId in index.

Is there a way to retrieve this list in Firebase? I am assuming that it is more efficient to retrieve a list of keys than a list with all the data from $categoryId.

I understand that an alternative way is to maintain an index list of all the categories, but this requires some more coding (when categories get edited and deleted).

I have a node in this form:

index
   $categoryId
     $productId

I wish to retrieve primarily a list of the keys of index, thus an object filled with all the available $categoryId in index.

Is there a way to retrieve this list in Firebase? I am assuming that it is more efficient to retrieve a list of keys than a list with all the data from $categoryId.

I understand that an alternative way is to maintain an index list of all the categories, but this requires some more coding (when categories get edited and deleted).

• javascript
• firebase
• nosql

1 Answer 1

You can use the shallow keys option in the REST API, but indexing is preferred.

Plnker demo.

fetch('<my-firebase-app>/category/.json?shallow=true')
  .then((response) => {
    return response.json()
  })
  .then((data) => console.log(data)) // prints only keys under category

Unfortunately, there's no solution in the realtime SDKs. But, I would remend structuring your data to avoid having to use the REST API. Try storing an index of $categoryId in your Firebase database. I know this is extra code, but it's usually a one-liner.

{
  "lookupCategory": {
    "category_one": true,
    "category_two": true,
    "category_three": true,
    "category_four": true,
    "category_five": true
  }
}

With this index, you can just do a realtime listen, or a .once() if preferred.

var ref = new Firebase('<my-firebase-app>/lookupCategory');
ref.on('value', (snap) => console.log(data));