StartAt(x) and EndAt(y) for pagination

[Dave Dawson]

I'm attempting to grab a number of records, but I'm pretty confused on how to do this. The end goal is to lazy-load notes in a list. So first off, I'd like to grab the first 15 records in a user's Notes list. Eventually I will grab the next 15 notes to append to the list.

I found this post, but it looks like this may be a different case. 

Ideally, I'd like to be able to do something like this:

var ref = firebaseRef.child('users/' + uid + '/notes');

var query = ref.orderByChild('date_updated').startAt(null, start).endAt(null, end);

Am I misunderstanding how startAt and endAt work? Is that second argument for the placement in the order of the `ref` array?

[Kato Richardson]

Hi Dave,

startAt() just takes one argument. See the query guide and the API doc for examples and usage. The second argument is for using a legacy feature (priorities).

If you want the first 15, then try startAt(start).limitToFirst(15).

☼, Kato

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[Dave Dawson]

Thanks for the quick response, Kato. 

How about the case where I'd like to get posts between 15-29? I'm not sure I understand how that works, based on that documentation.

startAt(15).endAt(29) doesn't seem to work.

[Kato Richardson]

For page 2, use startAt() the last value page 1. See this example, this example, and Firebase.util.Paginate.

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[Dave Dawson]

Firebase.util looks helpful. But is it ready to use in production? Is there a way to do this without adding an additional library?

[Kato Richardson]

Dave, check out the other links. One is a vanilla implementation.

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[Dave Dawson]

I missed that one. Thanks! But how about Firebase.util? Is that ready to use in production? 

I appreciate your quick responses. Thanks, again! It would be great if these kinds of things were documented in-depth somewhere so I don't have to bug you guys. :)

[Dave Dawson]

Looking through this example, I still have the same question as my first post. 

If I have a list of notes, each with unique keys. I want to get the 15th through 29th notes in that list. I don't know how to do that. .startAt(15).endAt(29) doesn't work, because that's looking for something different, maybe a key? But because each key is dynamically generated, I don't know what that will be. 

So how do I say: From the full list of notes, only grab the 15th through 29th notes?

Thanks

[Jethro Bodine]

I believe you'll have to know the keys at where you'd like to start. For the first page, a simple startAt().limitToFirst([number of results]). Then you'll have to store the key of the last record you pulled to start there next. Say for instance the pushId key for the last one is "txc56blp", I found a simple workaround* to start at the record right after is to add a character to the end of the string so it wont include the previous one... startAt('txc56blp0').limitToFirst(15).

*removing the last character of the key also works in reverse when wanting to endAt a certain point

Unfortunately firebase doesnt provide a simple numerical index yet, as attempting to do so would make the real-time nature much less performant is what I've been told in the past.

Hope that helps

[Dave Dawson]

Thanks so much for explaining that, Jethro. Much appreciated! 

I'll give that workaround a shot, but it seems pretty crazy that we need to do something like that to get what I thought would be a pretty simple query.