CODEWITHSUNDEEP
swiftfirebasefirebase-realtime-database
bibscy
bibscy

Reputation: 2718

How to query firebase data childByAutoID?

Is is possible to query this path in only one go and order the items by locality value (e.g London), but get only the items which are starting/ending at a certain childByAutoID?

Reason - when I scroll down in a tableView, I want to get from database more older items ordered by a certain area, e.g London and older than oldestKey which is the key of the media item.

The first batch of items is downloaded initially using .childAdded method.

Data:

 media
   -LgSsaqYzevONPTk2447 // <- childByAutoID
       caption: "12"
       locality: "City of London"
       mediaUID: "-LgSsaqYzevONPTk2447"

  -LgSsZnpSNLJwZBNgXGJ
       caption: "15"
       locality: "New York"
       mediaUID: "-LgSsZnpSNLJwZBNgXGJ"

Code

   class func observeNewMediaSingleTime(_ oldestKey: String,_ 
  userLocality: String, _ completion: @escaping ([Media], String?) -> Void) {


   let ref = Database.database().reference()
     let query = ref.child("media").queryOrdered(byChild: userLocality).queryStarting(atValue: oldestKey).queryLimited(toLast: 50)


 ref.observeSingleEvent(of: .value, with: { snapshot in

    guard snapshot.exists() else {
        completion([],nil)
        return}

     let firstItem = snapshot.children.allObjects.first as! DataSnapshot

      var arrayOfMedia = [Media]()

     var count = 0
     let enumerator = snapshot.children
     while let mediaItem = enumerator.nextObject() as? DataSnapshot {
        let media = Media(dictionary: mediaItem.value as! [String:Any])

        print("media.locality is \(media.locality)")
        //check if new media has same key as oldest post downloaded in previously
        if media.mediaUID != oldestKey{
            count += 1
            arrayOfMedia.append(media)
        }
    }//end of while
    arrayOfMedia.reverse()

    if count == arrayOfMedia.count {
        let updatedOldestKey = firstItem.key
        completion(arrayOfMedia, updatedOldestKey)
    }

})
}

Upvotes: 2

Views: 97

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 600141

If you know the locality value of the first item, this is possible with queryStarting(atValue:childKey:):

let query = ref.child("media")
  .queryOrdered(byChild: "locality")
  .queryStarting(atValue: "City of London", childKey: "-LgSsaqYzevONPTk2447")
  .queryLimited(toLast: 50)

So the above orders all child nodes by their locality, and then starts returning results at the with with locality="City of London" and key -LgSsaqYzevONPTk2447.

Upvotes: 2

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