Pagination

[sammy-SC]

It would be awesome to have pagination. For large data sets it is necessary.

[asciimike]

@sammy-SC yep, we're investigating the best way to do this (we'd really like a count aggregation function in the client first), as FirebaseUtil does it but not in an ideal way.

I think this was planned originally for right after authentication, as we'll need to add another array and some properties for tracking which items exist where.

[kermankohli]

Any updates on this? Also what would define a "large collection" - at what point does performance degrade due to a lack of paging?

[puf]

We're still working on other features. Pull-requests are always welcome.

[jhnferraris]

Any news about this feature?

[asciimike]

No, though I'm planning a refactor of the underlying data structure at some point and might get around to adding new features.

[kutakmir]

I see this as a huge limitation Firebase has. Seriously, this is making it useless for virtually any app with a longer list.
@mcdonamp @jhnferraris @kermankohli @sammy-SC @puf
I am new to Firebase and have very little time for this, but how about having a live session and put it together? I am available in CET working hours.

EDIT: feel free to ping me on skype: Haunebu512

[jhnferraris]

Hello,

We've tried doing our own pagination for Firebase. We've tried @timominous approach. See here (http://stackoverflow.com/questions/37430881/swift-ios-firebase-paging). Maybe this can help kick off the solution of the pagination problem.

[kutakmir]

Do you got it working correctly? Could you perhaps share the whole paginating solution with the rest of us?

[jhnferraris]

@kutakmir

Yes. We just followed the sample usage in the attached SO link.

var count = numberOfItemsPerPage

var query ref.queryOrderedByKey()

if startKey != nil {
  query = query.queryStartingAtValue(startKey)
  count += 1
}

query.queryLimitedToFirst(UInt(count)).observeSingleEventOfType(.Value, withBlock: { snapshot in
  guard var children = snapshot.children.allObjects as? [FIRDataSnapshot] else {
    // Handle error
    return
  }

  if startKey != nil && !children.isEmpty {
    children.removeFirst()
  }

  // Do something with children
})

The solution might depend on how the scrollable list would work but I think the same logic applies. Here's the pseudocode that we used:

1. If startKey is null, then it is page 1.
2. Somewhere in your model, save the key of the last of object of page 1 and set that to "startKey"
3. Use the value of startKey to get page 2, remove the first child since it will now be a duplicate with the last value of page 1.

[kutakmir]

How about the newly created, edited and removed items in the paginated list?

[asciimike]

I strongly recommend folks look at the FirebaseUtil Paginate API, as it has properly implemented all the child_* methods, and has a number of other useful features. Porting this over to iOS and Android is something that we'd love, and is something we think the community would benefit from--as Puf said, PR's are always welcome :)

[timominous]

@kutakmir Unfortunately, the logic provided in the SO link doesn't have listeners for events.

@mcdonamp I found this (googlearchive/firebase-util#51) and would like to think the team is already working on it. :) I would have to re-study JS if I'd have some time to port it over.

[asciimike]

@timominous that is in reference to this issue (though it wasn't exposed at the time), so just stay tuned to this thread for the latest :)