AngularFire2: query if child exists

Question

I'm planning on fetching a list from my database, where certain records contain a property that may be set. I want to query and display items which don't have this property

{
  books: {
    book_3: {
     title: "Return of The King"
    },
    book_2: {
     title: "The Two Towers"
    },
    book_1: {
     title: "The Fellowship of the Ring"
     read: 1256953732
    }
  }
}

I've read the first book and I want to display the remaining two books. In Firebase I do:

fbl.child('books').orderByChild('read').equalTo(null).on("value", function(data) { 
 // handle data
}

And in AngularFire2 I would do something like:

this.af.database.list('books', { query: {
  orderByChild: 'read',
  equalTo: null
}});

The first way works and I get book_2, book_3, but the AngularFire2 way returns the whole list! Is there a value that can be indicated as a null value? I've tried booleans, empty strings etc. but nothing seems to work.

Perhaps this is a bug.

It could be argued that it's a bug, as this is the test that's applied to the equalTo option. If null is a sensible value that's useful with the SDK, it should really only be ignoring undefined. I'd raise an issue. — cartant
– cartant, Commented Nov 29, 2016 at 22:32

cartant · Accepted Answer · 2017-02-05 03:12:57Z

1

~~The problem has been fixed with this pull request - which was included in the 2.0.0-beta.7 release of AngularFire2.~~

The problem has been fixed with this pull request - which should be included in the published version of AngularFire2 that follows 2.0.0-beta.7.

With the fix, if you create queries like this:

this.af.database.list('books', { query: {
  orderByChild: 'read',
  equalTo: null
}});

They will behave as you would expect them to and will return only the list items that don't have read properties.

edited Feb 5, 2017 at 3:12

answered Jan 31, 2017 at 9:01

cartant

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2 Comments

Bogac Over a year ago

has there been any changes lately that breaks this. I'm getting full list again, not with null eleminiation.

Bogac Over a year ago

"null elimination" is wrong term, but you get the problem.

Veer Singh · Accepted Answer · 2017-01-31 08:51:53Z

0

You could just populate the "read" child of every node with 0 ( as you are storing the timestamp and its an integer value) and query something like this:

   af.database.list('books', { query: {
orderByChild: 'read', 
    equalTo: 0
    }

answered Jan 31, 2017 at 8:51

Veer Singh

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