Find index of custom object in Firebase DataSnapshot array

Question

I have just started on Firebase.

Here is the JSON on Firebase :

{
  "messages" : {
    "-K2ib4H77rj0LYewF7dP" : {
      "name" : "anonymous",
      "text" : "Hello"
    },
    "-K2ib62mjHh34CAUbide" : {
      "name" : "anonymous",
      "text" : "I am fine"
    },
    "Test" : {
      "name" : "test111",
      "text" : "text22"
    }
  }
}

In Swift, I am observing when an item is added/removed on server, it should reflect in the app. Adding a record works fine. But for removing, I am not sure how to delete the item from the array based on index. Using indexOf returns a address (I guess array won't remove the object without mapping).

This is the incorrect code I have tried and does not work :

_refHandle = self.ref.child("messages").observe(.childRemoved, with: { [weak self] (snapshot) -> Void in
        guard let strongSelf = self else { return } 

        let values = snapshot.value as? NSDictionary
        let indexToBeRemoved = strongSelf.messages.index(where: {
            let valuesFilter = $0.value as? NSDictionary
            valuesFilter!["name"] as! NSString === values!["name"] as! NSString
            return true
        })
        print(indexToBeRemoved)
        strongSelf.messages.remove(at: indexToBeRemoved!)  
        strongSelf.clientTable.deleteRows(at: [IndexPath(row: indexToBeRemoved!, section: 0)], with: .automatic)    
    })

indexToBeRemoved comes out to be 0.

I also tried to simply remove the object using this answer but it returned an address.

Expected result :

Get the index of DataSnapshot object which is to be removed

Try to use functions that has `withPreviousSiblingWithKey`, something like `func observeSingleEvent(of eventType: DataEventType, andPreviousSiblingKeyWith block: @escaping (DataSnapshot, String?) -> Void)`, so you could get the key of the previous sibling, then it is easier to find the index of this key in your model array. (You can make it an array of tuples of "key, value", don't use dictionary, to preserve the arrangement) — user9335240, Feb 22 '18 at 12:30
To be able to identify the child to be removed you should compare its **key*, which is guaranteed to be unique. This means you need to store the key for each child into the array in `childAdded`, so that you can then look up that child's entry in the array when you get `childRemoved`. — Frank van Puffelen, Feb 22 '18 at 14:38

score 1 · Accepted Answer · answered Feb 22 '18 at 12:44

1

So this is what worked for me :

_refHandle = self.ref.child("messages").observe(.childRemoved, with: { [weak self] (snapshot) -> Void in
        guard let strongSelf = self else { return }

        let values = snapshot.value as? NSDictionary
        let indexToBeRemoved = strongSelf.messages.index(where: {
            let valuesFilter = $0.value as? NSDictionary
            return valuesFilter!["name"] as! NSString === values!["name"] as! NSString
        })

        print(indexToBeRemoved)
        strongSelf.messages.remove(at: indexToBeRemoved!)
        strongSelf.clientTable.deleteRows(at: [IndexPath(row: indexToBeRemoved!, section: 0)], with: .automatic)
    })

I returned the result of the comparison to the index.

But I believe this is not the best way to accomplish this. Since, in JSON, there might not be a unique key (I am taking name for comparison).
I would really like to see a better solution for this.

answered Feb 22 '18 at 12:44

Nitish

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**I am taking name for comparison** Don't use This. you can use your key **"-K2ib4H77rj0LYewF7dP"** it is safer. You can get this by **sanpshot.key** – Prashant Tukadiya Feb 22 '18 at 12:57
My suggestion to you is don't use NSDictionary & NSString if you are using swift3+. you can create model classes easily and fill all the data would be more easy – Prashant Tukadiya Feb 22 '18 at 13:00
@PrashantTukadiya : Noted. Thanks – Nitish Feb 22 '18 at 13:04
Value K2ib4H77rj0LYewF7dP is dynamic. – Nitish Feb 22 '18 at 13:05
Yes it is child by auto id. i am aware about it. still when child added or removed. you will get that key. – Prashant Tukadiya Feb 22 '18 at 13:07
strongSelf.messages... You never define it in your code. That's not a DatabaseReference object, is it? You should use a DatabaseReference object to remove a row, I suppose. – El Tomato Feb 22 '18 at 13:29

Find index of custom object in Firebase DataSnapshot array

1 Answers1